Data mappings for expert_disk

Add data mapping and variable for expert_disk mode in the Ubuntu
installer to be enabled or disabled when installing Ubuntu using
Cobbler.

Change-Id: I5e2c23cb350a1c7140f30324c946bab07e1d8514
Closes-Bug: #1325080
Merge remote-tracking branch 'cisco/icehouse' into bugs/1325080

Conflicts:
	data/data_mappings/common.yaml

Change-Id: I249ab78206f58a445da11d25aa9213b3e891e4d8
Merge pull request #93 from CiscoSystems/bugs/1325080

Data mappings for expert_disk