This unifies the three separate implementations of git() from
GitMakeShallowTest, GitShallowTest and GitLfsTest into one
implementation in FetcherTest. It also makes use of this in
FetcherLocalTest and FetcherNetworkTest.
(Bitbake rev: 8c8b418c3e6f8ab2535ad405e8006ee1012f3484)
Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>