Use openjdk by default for java element
Use openjdk by default for java element

Changes:
* add '-j' option for select java distribution
* use openjdk as java element by default

Change-Id: I740a2f7a39fbfeb96c9cc078b90a398d46c10cdb
Closes-bug: #1204957

crobby/sahara-image-elements,uladz/sahara-image-elements,bigfootproject/sahara-image-elements,openstack/sahara-image-elements,bigfootproject/sahara-image-elements,uladz/sahara-image-elements,openstack/sahara-image-elements,crobby/sahara-image-elements