common/rc: _scratch_mkfs_sized supports extra arguments

common/rc: _scratch_mkfs_sized supports extra arguments

To give more arguments to _scratch_mkfs_sized, we generally do as:

  MKFS_OPTIONS="-L oldlabel $MKFS_OPTIONS" _scratch_mkfs_sized $fs_size

to give "-L oldlabel" to it. But if _scratch_mkfs_sized fails, it
will get rid of the whole MKFS_OPTIONS and try to mkfs again.
Likes:

  ** mkfs failed with extra mkfs options added to "-L oldlabel -m rmapbt=1" by test 157 **
  ** attempting to mkfs using only test 157 options: -d size=524288000 -b size=4096 **

But that's not the fault of "-L oldlabel". So for keeping the mkfs
options ("-L oldlabel") we need, we'd better to let the
scratch_mkfs_sized to support extra arguments, rather than using
global MKFS_OPTIONS.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: fix string quoting issues]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>