Switch to using run-tox.sh everywhere.

Stop using run-unittests.sh. It creates confusion when people create
jobs. Instead standardize on run-tox.sh. This means rewriting all the
jobs that use run-unittests.sh to use run-tox.sh.

Note that this depends on the parent change to merge first and have all
our slave images rebuilt prior to merging this change.

Change-Id: Ib81403c25485b120f48080a59f1894dc2130c05f
Merge "Switch to using run-tox.sh everywhere."