Invoke the bash shell via /usr/bin/env so that these scripts run on operating systems without /bin/bash too.

TEST=run "git cl owners" on FreeBSD
BUG=

Review URL: https://codereview.chromium.org/197213008

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@274320 0039d316-1c4b-4281-b951-d872f2087c98