core: DiskImage Hierarchy cleanup

Make DiskImage and it's ancestors comply with java conventions:
Methods and data member names were altered, this redundant prefixes were
removed and value parameter in setters were renamed to meaningful names.
Also exchange use Of ArryaList to List when possible.

Change-Id: Iaf49ef042266187a6122ae4a667afd16d80efa52
Signed-off-by: Vered Volansky <vvolansk@redhat.com>