Add script to upload PGO profiles

Bug: http://b/120096099

Add a script to download profiles generated from automated profile
collection and commit them to git (in the toolchain/pgo-profiles
project).

This handles all projects with PGO enabled: skia, hwui, dex2oat,
hwbinder.

Sample Usage:
$ python update_profiles.py 500000 git_master ALL --profdata-suffix
2019-04-15

Additional/frequently-used arguments:
   -b BUG adds a 'Bug: <BUG>' to the commit message when adding the
          profiles.
   --do-not-merge adds a 'DO NOT MERGE' tag to the commit message to
                  restrict automerge of profiles from release branches.

Test: Test script with various options.
Change-Id: Ifcba5604e087ea82128bc8ea279bb47f1f80a89f
(cherry picked from commit 799180eedcbf36960cf52f5b96df0cc3277ff3c9)