Don't force use of the credential_store value for DB password.

[perfectra1n]

Currently, the ansible script forces use of the credential store's Nextcloud database password, even though currently this value is set within the playbook. If the value does not exist in user-defined values, a value is generated, placed in the credential store, and set for the playbook.

This commit utilizes the playbook's variable instead of forcing use of the credential store's.