Add SSML open/close tags to Speech Response
Add SSML open/close tags to Speech Response

SSML open/close tags are required in "speech" property of response
object for Assistant platform to recognize.

Change-Id: I58dcdd3b1ba9c4ca90279bf73c2c972ee49bc275

actions-on-google/actions-on-google-nodejs,actions-on-google/actions-on-google-nodejs,actions-on-google/actions-on-google-nodejs