mon: Fix default replicated pool ruleset choice

Specifically, in the case where the configured
default ruleset is CEPH_DEFAULT_CRUSH_REPLICATED_RULESET,
instead of assuming ruleset 0 exists, choose the lowest
numbered ruleset.

In the case where an explicit ruleset is passed to
OSDMonitor::prepare_pool_crush_ruleset, verify
that it really exists.

The idea is to eliminate cases where a pool could
exist with its crush ruleset set to something
other than a value ruleset ID.

Fixes: #8373

Signed-off-by: John Spray <john.spray@inktank.com>
(cherry picked from commit 1d9e4ac2e2bedfd40ee2d91a4a6098150af9b5df)

Conflicts:

	src/crush/CrushWrapper.h
XfsFileStoreBackend: call ioctl(XFS_IOC_FSSETXATTR) less often

No need to call ioctl(XFS_IOC_FSSETXATTR) if extsize is already set to
the value we want or if any extents are allocated - XFS will refuse to
change extsize in that's the case.

Fixes: #8241
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
(cherry picked from commit bc3b30ed09b8f3eb86b61e3a05ccacfd928faa95)