cephfs: add a test to ensure behavior of mixed use of Read + ReadAt
cephfs: add a test to ensure behavior of mixed use of Read + ReadAt

Add a test case to ensure the behavior of a mixed used [1] of Read
and ReadAt calls is consistent and ReadAt doesn't side effect
the file position used by Read.

1 - Not recommended, but we should not break now or in the future.

Signed-off-by: John Mulligan <eda8ad33169deab44f9fe65847f99e368da6c91b@redhat.com>

ceph/go-ceph,ceph/go-ceph,ceph/go-ceph