iotests: Fix status checks

An iotest's 'paused' condition is fickle; it will be reported as true
whenever the job is drained, for example, or when it is in the process
of completing.

030 and 041 contain such checks, we should replace them by checking the
job status instead.  (As was done for 129 in commit f9a6256b
for the 'busy' condition.)

Additionally, when we want to test that a job is paused on error, we
might want to give it some time to actually switch to the paused state.
Do that by waiting on the corresponding JOB_STATUS_CHANGE event.  (But
only if they are not already paused; the loops these places are in fetch
all VM events, so they may have already fetched that event from the
queue.)

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220324180221.24508-1-hreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>