Changes:
1. Add a variable in build.env for rook ceph cluster version.
2. Modify rook.sh so that it can deploy ceph cluster with
desirable version also rather than the one which rook installs
by default.
3. Remove the code which is no longer required:
a. Code which was added to test snapshot feature.
b. Code which was required because
https://github.com/rook/rook/pull/5925 was not fixed.
Signed-off-by: Mudit Agarwal <muagarwa@redhat.com>