Fix password not strong enough for identity test_groups

Use rand_password method to create users with more complex passwords.
This part was missed in commit I57649f5aac9b1abe1a9961d4b35479372ebee519

Change-Id: I9b06e4f1f026ab6795263969aa10e4ddfc5bae92
Related-Bug: 1448217
1 file changed