tests: Reducing sleep loops in ceph_objectstore_tool

tests: Reducing sleep loops in ceph_objectstore_tool

This python script is making excessive sleep calls while running some
ceph commands.

Waiting up to 5 seconds to get the proper health status can be shorten
to avoid the worst case of waiting almost 5 seconds for nothing.

This patch removes also two sleeps calls after a wait_for_health call
which is already supposed to provides a clean state. Waiting
respectively 20 & 15 seconds after that call is just loosing time which
is precious at make check time.

Signed-off-by: Erwan Velu <erwan@redhat.com>