Sanatize zpios-sanity.sh environment

Just like zconfig.sh the zpios-sanity.sh tests should run in a
sanatized environment.  This ensures they never conflict with an
installed /etc/zfs/zpool.cache file.

This commit additionally improves the -c cleanup option.  It now
removes the modules stack if loaded and destroys relevant md devices.
This behavior is now identical to zconfig.sh.

scripts/zpios-sanity.sh

@@ -64,6 +64,8 @@ fi
 
 # Perform pre-cleanup is requested
 if [ ${CLEANUP} ]; then
+	${ZFS_SH} -u
+	cleanup_md_devices
 	cleanup_loop_devices
 	rm -f /tmp/zpool.cache.*
 fi
@@ -148,6 +150,9 @@ DANGEROUS_CONFIGS=(					\
 	dm0-raid0					\
 )
 
+TMP_CACHE=`mktemp -p /tmp zpool.cache.XXXXXXXX`
+${ZFS_SH} zfs="spa_config_path=${TMP_CACHE}" || die "Unable to load modules"
+
 for CONFIG in ${SAFE_CONFIGS[*]}; do
 	zpios_test $CONFIG tiny
 done
@@ -158,4 +163,6 @@ if [ ${DANGEROUS} ]; then
 	done
 fi
 
+${ZFS_SH} -u
+
 exit $FAILS