[ITK] Updates to Gerrit Robot Builds

[Matt McCormick]

Hi folks,

Along with our recent Gerrit upgrade, we have also re-worked and
greatly improved the robot builds for proposed patches. The new system
uses the Gerrit Trigger plugin for Jenkins. Two Jenkins instances
currently will create robot builds, one on the Azure cloud for Linux
and Windows builds [1] and one at Kitware for MacOSX builds.

Improvements include:

- More builds executors with a more reliable uptime. The Azure builds
will now spin up and spin down on demand, and they stay up more
reliably. We now have two full-time MacOSX build executors.

- MacOSX builds are now running the latest version of XCode and
generating fully green build results.

- Remote Module submissions will have their module enabled during submission.

- Builds report when they are finished and add a +1 or -1 Verified
status automatically. It is much more useful to know when the builds
finish as opposed to when the builds start. The notification makes is
easier to know at a glance whether a patch builds cleanly. Links are
included to filtered CDash build results.  Links are also included to
the Jenkins jobs on Azure, which has a useful link to the full console
output.

- New and more extensive build controls. The following comments will
initiate builds:

  request build: all
  request build: windows
  request build: osx
  request build: linux
  request build: python

The 'request build: all' comment will generate Windows, MacOSX, and
Linux builds. The 'request build: python' comment will initiate builds
with Python wrapping.  These commands have been added and will be
updated on the Git development wiki page [2]

Happy testing :-),
Matt

[1] http://itkjenkins.cloudapp.net

[2] http://www.itk.org/Wiki/ITK/Git/Develop