Copy over git_utils from common and add GitLocalConfig

BUG=skia:5979

# Already ran tryjobs in https://skia-review.googlesource.com/c/4897/11
NOTRY=true
NOTREECHECKS=true
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4897

Change-Id: Iee061101b69b4d1cfb0e640785a19e42c6017ef8
Reviewed-on: https://skia-review.googlesource.com/4897
Commit-Queue: Ravi Mistry <rmistry@google.com>
Reviewed-by: Eric Boren <borenet@google.com>