iotests: Mark all tests executable

The majority of our iotests have the executable bit set; fix the
few outliers for consistency.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-id: 20180305161824.7188-1-eblake@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
10 files changed