pre-upload: Read .presubmitignore files.

Make look for .presubmitignore files
containing lists of relative-path wildcards, one per line,
matching files that should be excluded from common presubmit

TEST=manual: created a .presubmitignore file and uploaded a
     change to a powerd pref without getting nagged about a
     missing license

Change-Id: I3648e04ed840abd39d8a7fcc53fc7c65d27128ee
Reviewed-by: Dan Erat <>
Commit-Queue: Dan Erat <>
Trybot-Ready: Dan Erat <>
Tested-by: Dan Erat <>
2 files changed