fix:iOS Runloop cannot exit and other issues

doric-iOS/Pod/Classes/DoricContext.m

@@ -102,6 +102,9 @@ - (void)reload:(NSString *)script {
     [self.driver destroyContext:self.contextId];
     self.rootNode.viewId = nil;
     [self.rootNode clearSubModel];
+    [self.rootNode.view.subviews forEach:^(__kindof UIView *obj) {
+        [obj removeFromSuperview];
+    }];
     self.script = script;
     [self.driver createContext:self.contextId script:script source:self.source];
     [self init:self.extra];

doric-iOS/Pod/Classes/Engine/DoricJSEngine.m

@@ -103,6 +103,9 @@ - (instancetype)init {
 
 - (void)teardown {
     _destroyed = YES;
+    //To ensure runloop continue.
+    [self ensureRunOnJSThread:^{
+    }];
 }
 
 - (void)ensureRunOnJSThread:(dispatch_block_t)block {