Move login_unittest.py to cros_unittest.py so they run in the fyi waterfall.

The changes from login_unittest.py include:
* Removed testOobeLocalization since it's very specialized.
* Apply test.Enabled('chromeos')
* browser.Start() is no longer necessary.


BUG=NONE
TEST=manual
NOTRY=True

Review URL: https://codereview.chromium.org/183923029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255257 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255257