Show harvester version on console dashboard
* Add a new version variable `HarvesterVersion` to store version of
harvester. Console dashboard shows this version, instead of the
installer version.
* Add a new script `version-harvester` to determine and set up
`HARVESTER_VERSION` variable for later use.
* Update script `version`: Unset variable `DIRTY` in case it was set
somewhere else.
* Update script `build`:
- Pull harvester source from github if not exists. This will happen if
we're calling `make` from harvester-installer, but not from calling
`make build-iso` from harvester.
- Source "version-harvester" script to get the version of harvester.
- Update both harvester and harvester-installer version variables
using ldflags, `HarvesterVersion` and `Version` respectively.
Tested by calling `make` from harvester-installer and `make build-iso`
from harvester.
