fstests: teach _scratch_mkfs to handle mkfs option conflicts

Currently in _scratch_mkfs only xfs and ext4 could handle the mkfs
failure caused by conflicts between $MKFS_OPTIONS and mkfs options
specified by tests, because of _scratch_mkfs_xfs and
_scratch_mkfs_ext4. This is a very useful functionality that allows
tests to specify mkfs options safely and to test specific fs
configurations, without worrying about mkfs failures caused by these
options.

Now teach _scratch_mkfs to handle such mkfs option conflicts for
other filesystems too, i.e. mkfs again only with mkfs options
specified by tests. Also add the ability to filter unnecessary
messages from mkfs stderr.

Also update some btrfs tests to throw away _scratch_mkfs stdout,
because previously _scratch_mkfs did this for btrfs.

Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/btrfs/028

@@ -53,7 +53,7 @@ _supported_os Linux
 _require_scratch
 _require_btrfs_qgroup_report
 
-_scratch_mkfs
+_scratch_mkfs >/dev/null
 _scratch_mount
 
 _run_btrfs_util_prog quota enable $SCRATCH_MNT

tests/btrfs/121

@@ -56,7 +56,7 @@ _require_scratch
 
 rm -f $seqres.full
 
-_scratch_mkfs
+_scratch_mkfs >/dev/null
 _scratch_mount
 _run_btrfs_util_prog quota enable $SCRATCH_MNT
 # The qgroup '1/10' does not exist and should be silently ignored

tests/btrfs/122

@@ -55,7 +55,7 @@ rm -f $seqres.full
 
 # Force a small leaf size to make it easier to blow out our root
 # subvolume tree
-_scratch_mkfs "--nodesize 16384"
+_scratch_mkfs "--nodesize 16384" >/dev/null
 _scratch_mount
 _run_btrfs_util_prog quota enable $SCRATCH_MNT
 

tests/btrfs/123

@@ -55,7 +55,7 @@ _supported_os Linux
 _require_scratch
 _require_btrfs_qgroup_report
 
-_scratch_mkfs
+_scratch_mkfs >/dev/null
 # Need to use inline extents to fill metadata rapidly
 _scratch_mount "-o max_inline=2048"
 

tests/btrfs/126

@@ -51,7 +51,7 @@ _supported_os Linux
 _require_scratch
 _require_btrfs_qgroup_report
 
-_scratch_mkfs
+_scratch_mkfs >/dev/null
 # Use enospc_debug mount option to trigger restrict space info check
 _scratch_mount "-o enospc_debug"