CLOUDSTACK-6351 bugfix: Java1.6 is installed instead of Java7

Since epoch spesicifation doesn't work on RHEL6.3,
"java7" is used in the rpm spec.

Conflicts:
	packaging/centos63/cloud.spec
rbd: Create snapshot for cloning operations only when it is required

We used to create the snapshot after the copy from Secondary Storage,
but it could be that we never use the snapshot.

Now we check if the snapshot exists prior to performing the cloning operation