Clean up path in Sphinx complaint messages when using container

Here's an example message when building in the container with a syntax error and --verbose off:

Cleaning documentation build directory...
Done.
Building documentation...
/home/user/mounted_home/doc/source/tech_note/Crop_Irrigation/CLM50_Tech_Note_Crop_Irrigation.rst:168: WARNING: Explicit markup ends without a blank line; unexpected unindent. [docutils]
Documentation build completed, but with problems that must be resolved.
Re-run with --verbose for full output.

The messaging should strip /home/user/mounted_home/, because that path is NOT what the user would need to put in to edit the file. It's a path in the container only.

With verbose on, the original output is probably fine.