Make it work with 'coverage'.
Make FakeRepos initialization lazy. Only generate the repository when needed. It's in part intended for gclient_scm_tests.py but I left it out of this review.

To use:
  easy_install coverage
  ./tests/gclient_smoke.py -c
  coverage report

Current coverage with gclient_smoke:

Name                        Stmts   Exec  Cover
-----------------------------------------------
gclient                       557    416    74%
gclient_scm                   496    270    54%
gclient_utils                 195    117    60%
scm                           439    180    41%
(ignoring irrelevant files)

It's quite good in fact, 74% of gclient.py being executed with the smoke test.

Review URL: http://codereview.chromium.org/2352002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@48501 0039d316-1c4b-4281-b951-d872f2087c98