test: udisks on rhel-7-6 supports LUKS resizing now

Adjust the test accordingly.

Closes #9685

test/verify/check-storage-resize

@@ -109,12 +109,15 @@ class TestStorage(StorageCase):
                          can_grow=True, grow_needs_unmount=True)
 
     def testResizeLuks(self):
-        # No version of UDisks supports resizing encrypted block
-        # devices yet.  Once we get such a version, the buttons will
-        # automatically be enabled and this test needs to be adapted.
-        self.checkResize("luks+ext4",
-                         can_shrink=False,
-                         can_grow=False)
+        # Only newer versions of UDisks support resizing encrypted block devices
+        if self.machine.image in ["rhel-7-6"]:
+            self.checkResize("luks+ext4",
+                             can_shrink=True, shrink_needs_unmount=True,
+                             can_grow=True, grow_needs_unmount=False)
+        else:
+            self.checkResize("luks+ext4",
+                             can_shrink=False,
+                             can_grow=False)
 
 if __name__ == '__main__':
     test_main()