LU-4223 utils: fixing loop leaking in utils

LU-4223 utils: fixing loop leaking in utils

1. If the file is being opened by popen, it should use
pclose instead of fclose to close the file, to make sure
the process created by popen is closed after pclose, then
to avoid loop device is being hold on release.

2. Give another try in loop_cleanup in case there are still
some process going on with the loop.

3. wait loop device to release before continue conf-sanity
32c.

4. Add losetup -a to list loop dev information when the
test(conf-sanity 32) fails.

This patch is back-ported from the following one:
Lustre-commit: 98ac0fe3a45dde62759ecaa4c84e6250ac2067f8
Lustre-change: http://review.whamcloud.com/8409

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes \
mdscount=4 mdtcount=4 testlist=conf-sanity

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ic1ebc2a6b2ce4280c2123080171e203e99267b28
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: http://review.whamcloud.com/8723
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>