This functions waits for at least 2 times hbase.master.wait.on.regionservers.interval, defaulted at 3 seconds, i.e. 6 seconds for every mini hbase cluster starts.
In the context of a mini cluster, it's not useful, as the regions servers are created locally.
Changing this to a lower value such as 100ms gives 5.8 second per HBase cluser start. It should lower the build time on the apache server by more than 8%.
Beeing more aggressive (removing all the wait time) could be possible as well. To be studied later.