Fixes incorrect assertion check

assertNotIn/assertIn does not work if the second
variable is of type List of dictionaries.
Suppose if it of only dictionary type, it will try
to match only 'key' but not 'value'.
Hence, the assertion check done here is not correct.

This patch fixes an incorrect assertion check for
"BasicOperationsImagesTest.test_delete_image" test

Change-Id: I7058d209cc92a2e381308e59e07d180e84bde182
Closes-Bug: #1346757
Merge "Fixes incorrect assertion check"