support/testing: check ubi image before booting

Do the same as other fs tests and minimally check the ubi image before
booting.
The call to 'file' was already there, but the output wasn't tested for
some unknown reason. Add the assert for the output of the command.

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

support/testing/tests/fs/test_ubi.py

@@ -25,6 +25,7 @@ class TestUbi(infra.basetest.BRTest):
                                       cwd=self.builddir,
                                       env={"LANG": "C"})
         out = out.splitlines()
+        self.assertIn("UBI image, version 1", out[0])
 
         subprocess.call(["truncate", "-s 128M", img])