Previously if one or both of these values were unset, the tests would simply fail
because `git config` returns 1.

R=dpranke@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/18053009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@208966 0039d316-1c4b-4281-b951-d872f2087c98