block/rbd: add 'namespace' to qemu_rbd_strong_runtime_opts[]

block/rbd: add 'namespace' to qemu_rbd_strong_runtime_opts[]

Commit 19ae9ae014 ("block/rbd: Add support for ceph namespaces")
introduced namespace support for RBD, but we forgot to add the
new 'namespace' options to qemu_rbd_strong_runtime_opts[].

The 'namespace' is used to identify the image, so it is a strong
option since it can changes the data of a BDS.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1821528
Fixes: 19ae9ae014 ("block/rbd: Add support for ceph namespaces")
Cc: Florian Florensa <fflorensa@online.net>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20200914190553.74871-1-sgarzare@redhat.com>
Reviewed-by: Jason Dillaman <dillaman@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>