generic: assign a number of tests to attr group

generic: assign a number of tests to attr group

A few generic tests have a _require_attrs runtime check for support
of extended file attributes by a tested filesystem, review shows that
the tests listed below are definitely using extended file attributes,
thus this implies that the tested filesystem should provide support of
the feature in general.

Adding the tests explicitly to attr group of tests allows to get a better
granularity of selecting or deselecting tests by groups in accordance to
extended file attributes feature given by a filesystem, the change affects
the next list of tests:

  * generic/037
  * generic/066
  * generic/103
  * generic/337
  * generic/449

Signed-off-by: Vladimir Zapolskiy <vladimir@tuxera.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>