Bugfix for WSREP SST auth config typo

[elcomtik]

Description

When I implemented the WSREP SST auth configuration I made a typo for the default value of wsrep_sst_auth. It is currently set to the variable used to configure MySQL user instead of pair [username]:[password]. The default value for wsrep_sst_auth should be set to:

wsrep_sst_auth="{{ mariadb_sst_username }}:{{ mariadb_sst_password }}"

This issue passed through tests because they do not cover the scenario of using mariabackup SST nor TLS encrypted SST. I do not intend to implement it now, maybe someday when more people will use these features.

Related Issue

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• I have run the pre-merge tests locally and they pass.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.