Configure grpc connection params in xds client

The xdsclient today doesn't have the correct grpc params.
Few params we should explore are: ([link](https://github.com/grpc/grpc-go/blob/master/dialoptions.go))
1. should the connection creation be blocking
2. retry policy
3. secure connection
4. [connection management](https://github.com/grpc/proposal/blob/master/A9-server-side-conn-mgt.md)
5. explore other default params a grpc connection should have.