test-lchown, test-chown: also skip test if lchown/chown fails with EPERM

test-lchown, test-chown: also skip test if lchown/chown fails with EPERM

These tests abort on FAT file systems right after the test for
filtering out situation without ownership support; errno is EPERM
in such a case.

* tests/test-lchown.h (test_lchown): Add EPERM to the condition to
skip this test.
* tests/test-chown.h (test_chown): Likewise.