_check_sids previously grepped the entire output of dm_getall_sessions for sids,...

_check_sids previously grepped the entire output of dm_getall_sessions for sids, which is:
ret=dm_getall_sessions return value
rnelem=number of sessions
sids="sid1 sid2 ... sidn "

If the session id of a previously destroyed session matches the current number of sessions (rnelem),
then _check_sids() $PREV_DESTROYED_SID will _not_ flag ERROR: SID(s) not created.

This fix also makes _check_sids() not rely on sids being consecutive. DMF may be running on a FS in background.

Tested on Linux and Irix.
Merge of master-melb:xfs-cmds:28043a by kenmcd.

  change _check_sids to go through sids line 1 by 1 checking for matches