SampleApplication: Update user passwords

OPENIG-4825 implies the modification of the AM password as now the policy is more strict on the AM side(due to DJ 7.0.0-M2020-10.7), and does not allow anymore weak passwords, even for testing.

Once the password will be changed in documentation for user george costanza,

We must update the Sample application files, to align with the AM new password's policy.

• common.js (used for UMA)
• credentials.properties (sample application login)

Note that some unit tests may also reflect that change(but this is only cosmetic, to be homogeneous with the password policy update).