iotests: Skip test 079 if it is not possible to create large files

Test 079 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. Test 079 tries to
create a 4G sparse file, which is apparently already too big for these
containers, so check first whether we can really create such files before
executing the test.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/079

@@ -39,6 +39,9 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
 _supported_fmt qcow2
 _supported_proto file nfs
 
+# Some containers (e.g. non-x86 on Travis) do not allow large files
+_require_large_file 4G
+
 echo "=== Check option preallocation and cluster_size ==="
 echo
 cluster_sizes="16384 32768 65536 131072 262144 524288 1048576 2097152 4194304"