feat(base/connection): log leave failure reason

Because there are multiple reasons on why a conference.leave() may fail
it's helpful to know if and why it happened.

react/features/base/connection/actions.native.js

     SET_LOCATION_URL
 } from './actionTypes';
 
+const logger = require('jitsi-meet-logger').getLogger(__filename);
+
 /**
  * The error structure passed to the {@link connectionFailed} action.
  *
 
             promise
                 = conference_.leave()
-                    .catch(() => {
+                    .catch(error => {
+                        logger.warn(
+                            'JitsiConference.leave() rejected with: ',
+                            error);
+
                         // The library lib-jitsi-meet failed to make the
                         // JitsiConference leave. Which may be because
                         // JitsiConference thinks it has already left.