Add support for custom provider implementation

- Add a set_provider_factory() method to server_state to allow
  injecting provider factory which will be called when the
  provider is loaded.

Other related changes:
- Implement to_string() helper method for id class.
- Fix id ostream operator human readable id printing.
- Pass victim client_service as an argument to provider::bf_abort()
  to allow passing victim context to custom provider.
- Implement prev() helper method for seqno class.
- Make server_state recover_streaming_appliers_if_not_recovered()
  public. In some recovery scenarios the method must be called outside
  of server_state internal code paths.
- Add storage_service requires_globals() method. The storage service
  implementation may override this to return false if changing to
  storage service context does not require store/reset globals.
- Change view final() to also require that the view status is not
  primary for the view to be final. Also change the method name to
  is_final() to avoid confusion with C++ final identifier.
- Fixes to server state handling in disconnecting and disconnected
  states.
- Keep TOI meta data over whole TOI critical section.

Co-authored-by: Denis Protivensky <denis.protivensky@galeracluster.com>

include/wsrep/id.hpp

@@ -93,6 +93,11 @@ namespace wsrep
         {
             return undefined_;
         }
+
+        /**
+         * Return id in string representation.
+         */
+        std::string to_string() const;
     private:
         static const wsrep::id undefined_;
         native_type data_;