Create a git manifest from source-repositories

As git repositories are copied into the image make a note of their
details and add them to a manifest on the build system.

This allows the code used in building an image to be found after
the image build is completed without needing to open the image up
for inspection.

Change-Id: I7dbe9e163ad38a418cf2869a81e720de2c27dfb1
Merge "Create a git manifest from source-repositories"