Improve CDCR Tests; create factory methods to avoid redundancy

There are multiple methods in CdcrBidirectionalTest introduced SOLR-11003, can be used to create tests for other improvements like SOLR-12057, SOLR-12071 where we need to test multiple combinations of NRT, TLOG and PULL replicas.

This JIRA tracks refactoring of test classes to create common framework methods, and improve the redundant code and remove thread sleeps if not necessary.