Tell Git to ignore GT.M JOB command output files

The GT.M JOB command leaves child process stdout/stderr in .mjo/.mje
files.  Ignore the files in case they appear from processes run under
the source tree checkout.

Change-Id: I7b363ff2e8aa02cb0adeafce5b1c3dfb28ee9961
Merge "Tell Git to ignore GT.M JOB command output files"