This element adds python-brick-cinderclient-ext to the make customized image
to support cinder local attach/detach functionality. Currently it has the
dependency on known bug<https://launchpad.net/bugs/1623549>, which would be
resolved with next release of python-brick-cinderclient-ext.
Change-Id: Idfe83bafa2843c781c18b83f1a3aece3ae852f78
