Explicitly create a git config in the test repos.

Explicitly create a git config in the test repos.

Committed: https://code.google.com/p/dart/source/detail?r=14052

[Bob Nystrom, 2012-10-25 00:13:30]

The last patch didn't seem to do the trick so let's try something more
gratuitous.

[nweiz, 2012-10-25 00:20:12]

lgtm