Start libification of jjb

Allow the expansion of the jjb template language yaml into a list before
generating xml. This will allow others to consume the template parts of
jjb without forcing them to be tied to xml.

Change-Id: Ifd99151f8246eb817194adc2180189f739ccf742
Added description for node attribute in documentation.

The "node" attribute of Job allows to specify labels of Jenkins
builders where the job can be executed.

Change-Id: Icb2a72a3d6340b1f9d9bdcc27e2e9691b1752c24
Merge "Added description for node attribute in documentation."
Merge "Start libification of jjb"