Let test-auth.py assign permanent password

[Lsquared13]

The test-auth.py script should be able to set a permanent password instead of only a temporary one.

Here's what I think needs to happen:

• Add a --password required argument to the create command
• Modify the call to admin_create_user to include a TemporaryPassword argument. This argument should be a hard-coded 'magic password' which is complex enough to not fail on a reasonable password_policy (e.g. At least 12 characters including uppercase, lowercase, numerical, and special symbol characters)
• Add another call to the Cognito API which executes a change password challenge and changes the password to the specified value in the --password argument.

Additionally, we should modify the README to reflect that the password no longer needs to be changed through the web browser

[Lsquared13]

Doing temporary password instead