xfstests: use value of FSTYP if defined externally

The initial value of FSTYP is unconditionally set to 'xfs' and the
filesystem type is taken from the TEST_DEV. This could lead to confusion
if the device hasn't been formatted yet, eg. an empty image in VM, or
a different test setup took place before.

Now one can specify the desired FSTYP in advance and be safe. If unset,
the fallback to TEST_DEV type continues to work.

Signed-off-by: David Sterba <dsterba@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

check

@@ -33,7 +33,6 @@ showme=false
 have_test_arg=false
 randomize=false
 here=`pwd`
-FSTYP=xfs
 xfile=""
 
 # start the initialisation work now
@@ -57,10 +56,12 @@ then
     exit 1
 fi
 
-# Autodetect fs type based on what's on $TEST_DEV
-if [ "$HOSTOS" == "Linux" ]; then
+# Autodetect fs type based on what's on $TEST_DEV unless it's been set
+# externally
+if [ -z "$FSTYP" -a "$HOSTOS" == "Linux" ]; then
     FSTYP=`blkid -c /dev/null -s TYPE -o value $TEST_DEV`
 fi
+FSTYP=${FSTYP:=xfs}
 export FSTYP
 
 SUPPORTED_TESTS="[0-9][0-9][0-9] [0-9][0-9][0-9][0-9]"