provide native MySQL behavior when no replication provider

[Seppo Jaakola]

All replication 'hooks' are skipped when there is no replication provider loaded. However, there are certain wsrep patch code paths, which remain effective and 100% native MySQL behavior is not guaranteed.
The task is to make sure that when there is no replication provider, no wsrep functionality will be executed.

For verification, all MySQL test suite tests must pass when running without replication provider

[Seppo Jaakola (seppo-jaakola)]

Pushed a fix (#3549), which provides following logic:
* when wsrep_on (session or global) is not set, all wsrep code is skipped
* when wsrep_provider='none', the 'dummy' provider stub is active, wsrep hooks will be called, but they will do nothing
* setting wsrep_provider to 'none' will implicitly set also wsrep_on=0 and wsrep_cluster_address=NULL, this is native MySQL mode
* setting wsrep_provider to some real provider value, will implicitly set also wsrep_on=1

[Seppo Jaakola (seppo-jaakola)]

with the fix for lp:856155, wsrep patched mysqld should behave like native mysql server