iotests: Skip test 060 if it is not possible to create large files

iotests: Skip test 060 if it is not possible to create large files

Test 060 fails in the arm64, s390x and ppc64le LXD containers on Travis
(which we will hopefully enable in our CI soon). These containers
apparently do not allow large files to be created. The repair process
in test 060 creates a file of 64 GiB, so test first whether such large
files are possible and skip the test if that's not the case.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>