improve tests for mask_password and mask_dict_password
improve tests for mask_password and mask_dict_password

All the tests used a very 'strong' password of mypassword and it
wasn't apparent in reviewing some new tests whether the masking was
being done of the 'word' password in mypassword or the command option
or dictionary key.

So I've taken the liberty to rewrite all the tests with a better
password.

Change-Id: I50c05d79bc9d8eaae5147d7f96ef5abfd0f2b2e1

openstack/oslo.utils