fstests: add module reloading helpers

Add some helper functions to require that we can reload a given
module, and add a helper to actually do that.  Refactor the existing
users to use the generics.

We need to hoist completely the behaviors of the old btrfs module
helper because we need to confirm before starting the test that we
actually can remove the module.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/btrfs/125

@@ -54,6 +54,7 @@ _cleanup()
 # get standard environment, filters and checks
 . ./common/rc
 . ./common/filter
+. ./common/module
 
 # remove previous $seqres.full before test
 rm -f $seqres.full
@@ -63,10 +64,8 @@ rm -f $seqres.full
 _supported_fs btrfs
 _supported_os Linux
 _require_scratch_dev_pool 3
-
-# we need btrfs to unload, need test dir unmounted
 _test_unmount
-_require_btrfs_loadable
+_require_loadable_fs_module "btrfs"
 
 _scratch_dev_pool_get 3
 
@@ -118,7 +117,7 @@ echo "unmount" >> $seqres.full
 _scratch_unmount
 echo "clean btrfs ko" >> $seqres.full
 # un-scan the btrfs devices
-_reload_btrfs_ko
+_reload_fs_module "btrfs"
 _mount -o degraded,device=$dev2 $dev1 $SCRATCH_MNT >>$seqres.full 2>&1
 dd if=/dev/zero of="$SCRATCH_MNT"/tf2 bs=$bs count=$count \
 					>>$seqres.full 2>&1
@@ -154,7 +153,7 @@ echo "Mount degraded but with other dev"
 
 _scratch_unmount
 # un-scan the btrfs devices
-_reload_btrfs_ko
+_reload_fs_module "btrfs"
 
 _mount -o degraded,device=${dev2} $dev3 $SCRATCH_MNT >>$seqres.full 2>&1