common/xfs: Initialise OPTIND for getopts calls

According to the bash man page:

	OPTIND is initialized to 1 each time the shell or a shell
	script is invoked.

This doesn't appear to be true - in tests scripts with no other
getopts calls, I'm seeing the getopts loop in _xfs_check to fail to
parse input parameters correctly. Tracing shows the parameters are
being passed to _xfs_check correctly, but on occassion getopts
simply doesn't see them.

Hence when running tests with both external log and real time
devices, tests are failing at random because xfs_check is
mis-parsing the parameters passed to it and not configuring the
external log correctly:

_check_xfs_filesystem: filesystem on /dev/sdg is inconsistent (c)
*** xfs_check output ***
aborting - no external log specified for FS with an external log
*** end xfs_check output

Fix this by ensuring OPTIND is correctly initialised before using
getopts. Do it for all places that call getopts that don't already
set OPTIND=1 before starting their parsing loop.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/generic/074

@@ -87,6 +87,7 @@ _usage()
 
 _process_args()
 {
+    OPTIND=1
     while getopts "f:l:n:?" c $@
     do
         case $c

tests/generic/075

@@ -98,6 +98,7 @@ _usage()
 
 _process_args()
 {
+    OPTIND=1
     while getopts "l:n:N:?" c $@
     do
         case $c

tests/generic/112

@@ -94,6 +94,7 @@ _usage()
 
 _process_args()
 {
+    OPTIND=1
     while getopts "l:n:N:?" c $@
     do
         case $c