SCM module: Add support for multiple Git remotes.

Configuring multiple Git remotes is necessary to allow Jenkins to
merge commits from a remote branch into a local branch. Note that
this is not the same as specifying multiple SCMs which are cloned
into separate directories.

Change-Id: Ifef2da85fa22a979570d4ea2b6f30d4bd37da116
README.rst: Add links

Change-Id: Ia784781c9142f7a9deaeef812c6c95a936342f3a
Merge "README.rst: Add links"
Merge "SCM module: Add support for multiple Git remotes."