For XFSQA test 018 081 082 095 the test specifies test wide mkfs options using MKFS_O...

For XFSQA test 018 081 082 095 the test specifies test wide mkfs options using MKFS_OPTIONS env var.
Further mkfs options are then appended by _mkfs_log at mkfs time with _scratch_mkfs_xfs.

Currently there are a few ways mkfs options are specified in XFSQA:
1) suite wide MKFS_OPTIONS are specified before tests are run
        e.g.
        vimes:/home/fsgqa/kali/xfsqa/xfstests # export MKFS_OPTIONS="-l size=100m"

2) test wide MKFS_OPTIONS are specified during a particular test
        e.g. 119
        export MKFS_OPTIONS="-l version=2,size=1200b,su=64k"

3) mkfs options are appended by a test at mkfs time
        e.g.  083
        _scratch_mkfs_xfs -dsize=$fsz,agcount=$ags  >>$seq.full

(4) Another form of appending is just appending to MKFS_OPTIONS directly
        e.g.    114:export MKFS_OPTIONS="$MKFS_OPTIONS -i parent=1"
                115:export MKFS_OPTIONS="$MKFS_OPTIONS -i paths=1"

e.g. Methods (2) *and* (3) for specifiying mkfs options are used in these tests.
This causes problems, because the mkfs options fallback code assumes the
_mkfs_log _scratch_mkfs_xfs appended options are the only test specified options.

This change causes tests using _mkfs_log to only use option (2).
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Merge of master-melb:xfs-cmds:29031a by kenmcd.