qa/workunits/rbd/cli_generic.sh: narrow race window

qa/workunits/rbd/cli_generic.sh: narrow race window

... when checking whether a rbd_support module command fails after
blocklisting the module's client.

In tests that check the recovery of the rbd_support module after its
client is blocklisted, the rbd_support module's client is
blocklisted using the `osd blocklist add` command. Next,
`osd blocklist ls` command is issued to confirm that the client is
blocklisted. A rbd_support module command is then issued and expected
to fail in order to verify that the blocklisting has affected the
rbd_support module's operations. Sometimes it was observed that before
this rbd_support module command reached the ceph-mgr, the rbd_support
module detected the blocklisting, recovered from it, and was able to
serve the command. To reduce the race window that occurs when trying to
verify that the rbd_support module's operation is affected by client
blocklisting, get rid of the `osd blocklist ls` command.

Fixes: https://tracker.ceph.com/issues/63673
Signed-off-by: Ramana Raja <rraja@redhat.com>
(cherry picked from commit ea033fe8607c2b31892536afc3f08f3009b24139)