`spfs clean` fails if disk is full

[jrray]

When the local spfs repository is located on a disk that is very full, spfs clean will fail with "No space left on device" if the user running the command does not already have a renders directory. As the only way to open a local repository is to ultimately create it, this involves attempting to create a number of directories, including the per-user renders directory.

This has to be worked around by either running the clean as a different user that already has a renders directory, or manually removing some files to free up enough space to let clean run normally.

The clean command has no need for that renders directory to exist, but there is currently no way for clean to just open an existing repo in a "read only" way.

[rydrman]

From the meeting today:

• the solution is likely some kind of type state or other delayed creation of the renders area until the logic flow requires it. Ie the clean code would never invoke that portion because it never tries to render anything.

[jrray]

#1159 will address this issue.