Set is_public to False by default for volume backed snapshots

This update results in the same behavior that is already implemented
in _create_image where the meta_data for is_public is set to False.

Change-Id: Ie0720d5c847871527db7d9477ca6cb05abe7a1a5
Closes-Bug: #1255316
Pass rbd_user id and conf path  as part of RBD URI for qemu-img

Unlike rados.py, qemu-img does not use id from CEPH_ARGS and has to be
given a ceph user id and conf path explicitly in RBD URI

Closes-Bug: #1261675
Change-Id: I9226515f2a860ed45d12012fd5b6bc7e842f6d32
Consolidate the blockdev related filters

Seeing a "/usr/local/bin/nova-rootwrap: Unauthorized command" error
in the logs when  "blockdev --flushbufs" is executed because of the
existing blockdev in compute.filters. We need to merge both into a
single RegExpFilter

Change-Id: Ic323ff00e5c23786a6e376e67a4ad08f92708aef
Merge "Pass rbd_user id and conf path  as part of RBD URI for qemu-img"
Merge "Set is_public to False by default for volume backed snapshots"
Merge "Consolidate the blockdev related filters"