add rocksdb bz2 dep

Signed-off-by: Sage Weil <sage@redhat.com>
debian, rpm: build require bzip2 dev

Signed-off-by: Sage Weil <sage@redhat.com>
configure: check for c++11 but do not enable it

Signed-off-by: Sage Weil <sage@redhat.com>
debian, rpm: build rocksdb statically if we can

Signed-off-by: Sage Weil <sage@redhat.com>
os/FileStore: store omap_backend type in FSSuperblock

The only time we set this is at mkfs time.  Thereafter, we stick with the
same backend.

Signed-off-by: Sage Weil <sage@redhat.com>