Fix tst-pkey expectations on pkey_get [BZ #23202]

From the GNU C Library manual, the pkey_set can receive a combination of
PKEY_DISABLE_WRITE and PKEY_DISABLE_ACCESS.  However PKEY_DISABLE_ACCESS
is more restrictive than PKEY_DISABLE_WRITE and includes its behavior.

The test expects that after setting
(PKEY_DISABLE_WRITE|PKEY_DISABLE_ACCESS) pkey_get should return the
same.  This may not be true as PKEY_DISABLE_ACCESS will succeed in
describing the state of the key in this case.

The pkey behavior during signal handling is different between x86 and
POWER.  This change make the test compatible with both architectures.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>