Add repo scm

Add support for 'repo' plugin from Android development. Ensure
only settings that actually are required are written out to
the produced XML, and all optional settings aren't included
unless explicitly set.

Change-Id: I662bdd4d348ce7ec7d213e5d7149daf130fda697
Add optional option to copyartifact plugin

Simply add the optional option to the copyartifact plugin that was
missing. It comes with a small pieces of doc and related tiny
relevant sample.

Change-Id: Ib74932bd9e0a988b826547badd02c8a1c67ae138
Closes-Bug: #1236909
Merge "Add repo scm"
Merge "Add optional option to copyartifact plugin"