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
Add support for multiple Gerrit servers in Gerrit trigger

Since version 2.11.0 the Gerrit Trigger Plugin can be configured
to trigger on more than one server.

Change-Id: I2082c5cfd14cd2494e2a7192beeb4909552cb7f6
Added support for Exclusion plugin

This plugin allows the specification of critical blocks for builders.
Once a set of builders is "wrapped" by a critical block start/critical
block end pair, any resources (string) specified in the exclusion build
wrapper will cause any jobs with those same resources to block and allow
only one of those builds to proceed at a time.

Change-Id: I0bf4ab003709917aa7fe6ad57b31200f466658da
Merge "README.rst: Add links"
Merge "SCM module: Add support for multiple Git remotes."
Merge "Add support for multiple Gerrit servers in Gerrit trigger"
Merge "Added support for Exclusion plugin"