Make NUOPC the default driver rather than MCT. Update externals and switch
tests so nuopc tests are explicit for mct. Fix several issues. Update the README
files and in-place documentation.

Remove MODEL as a setting for the build system, use COMP_NAME instead.
Adds a container machine definition in cime.

See README.NUOPC_driver.md at the top level for a description of what changes.

Resolved Conflicts:
doc/ChangeLog
doc/ChangeSum
src/soilbiogeochem/SoilBiogeochemDecompCascadeCNMod.F90

This tag provides the FATES model access to the fcansno variable to facilitate a correction
of it's radiation transfer code.

Resolved conflicts:
doc/ChangeLog
doc/ChangeSum

Correct perched water table calculation

Modifies the calculation of the frost table and perched water table
layers.

This brings in the answer-changing aspects of the Hillslope Hydrology
branch (ESCOMP#1715).

Specific changes are:

* PerchedWaterTable

1) Frost table depth

a) original frost table determination looped from the top
of the soil column downward to the index of the first layer
whose temperature was <= freezing, and whose neighbor above
had a temperature above freezing.  The frost table depth is
then given by the node of that soil layer, i.e. z(k_frz).

b) in the new method, the same index is found, but the
depth of the frost table is given by the depth of the top
of the frozen layer, i.e. zi(k_frz-1).  Note zi(k_frz) would
be the bottom of layer k_frz.

2) Perched water table depth

a) in the original formulation, a loop from k_frz to layer 1
was used to identify the deepest layer in 1:k_frz whose
volumetric soil moisture was greater than a threshold given
by sat_lev (e.g. sat_lev = 0.9).

b) in the new method, the search is only done if k_frz is
greater than 1.  The rationale is that if k_frz = 1, then
zwt_perched has already been initialized to the frost_table
depth (which is equal to the top of the uppermost soil layer),
and therefore no search is required.

3) Determining perched water table depth within layer
identified by index k_perch in 2)

a) in the original formulation, the perched water table
depth was calculated by linearly interpolating between layers
k_perch and k_perch+1, with no consideration of their relative
values.  In the case where the deeper layer was drier than the
layer above it, this could result in values far outside the
soil layer.

b) in the new formulation, if the deeper layer is drier than the
layer above it (s1 > s2), then the perched water table depth is
simply given by the depth of the upper surface of layer k_perch,
i.e. zi(c,k_perch-1).

* PerchedLateralFlow

1) Removal of icefrac calculation

a) in the original calculation, the frozen layer was included,
so an ice impedance factor was calculated using icefrac.  If
only unfrozen layers are used, no ice impedance factor is needed.

b) in the new formulation, the icefrac variable and loop are
removed.

2) Move loop calculating frost and perched water table depths

a) in the original formulation, the frost and perched water
table depths were calculated in the same loop as the calculation
of the lateral flow from the perched saturated zone.

b) in preparation for the hillslope hydrology branch, this
calculation is moved into its own loop.

3) q_perch calculation

a)in the original formulation, q_perch was calculated by summing
over layers k_perch to k_frost.  However, because k_frost is now
identified as the frozen layer, and its depth the top of the frozen
layer, it should not be included in the calculation; only the
unfrozen layers above it should be included.

b) in the new formulation, the loop is bounded by k_frost-1 instead
of k_frost.

4) Removal of water from perched saturated zone

a) the in the original method, the frozen layer (k_frost)
was included in the loop.  Also, the drainage was defined to be
negative, which was confusing.

b) in the new method, the frozen layer is not included in the
loop; water is only removed from the unfrozen layers above k_frost.
Calculate drainage as positive values, which are then subtracted
from the soil moisture in each layer.

Resolved conflicts:
doc/ChangeLog
doc/ChangeSum

Reuse some files generated in initialization when rerunning

A new directory is now in your run directory init_generated_files. These
two run time generated files - finidat_interp_dest.nc and the land
fraction file ctsm_landfrac.nc (which is new in this PR) - are put in
that directory when they are created. Then, if they already exist, they
are reused rather than being regenerated. (Technically, it looks for a
status file that flags successful creation of this file.) This applies
when you rerun a startup (non-restart) run a second or subsequent time,
as is common when doing development and testing.

For tests, theinit_generated_files directory is removed before running,
so that rerunning a test will do the same thing the second time.

There are occasional, rare cases when a user would need to manually
remove the init_generated_files directory – e.g., when changing things
about N dominant landunits or PFTs.

Also, output was cleaned up in a few cases so that it did not span
multiple lines.

Resolved conflicts:
doc/ChangeLog
doc/ChangeSum