MFC r321949,r321950,r322101:

r321949:

Add expected failures for ZFS

• :f_flag fails on ZFS because UF_IMMUTABLE isn't supported [1].
• :v_flag fails on ZFS because the mode for foo is [always] updated unnecessarily.

get_filesystem(..) (supporting function that was added to the test script)
is based on equivalent logic in usr.bin/extattr/tests/extattr_test.sh .

PR: 221189 [1], 221188 [2]

r321950:

Always use first parameter passed to get_filesystem(..) instead of discarding it
and using . instead.

MFC with: r321949
PR: 221189 [1], 221188 [2]

r322101:

Don't check result of chflags in f_flag_cleanup()

This will prevent false positives from occurring if the test is run on
ZFS since ZFS doesn't support fflags throbbing like UFS.

PR: 221189
MFC with: r321949