WebRTC.MediaHandler#getDescription: promisify mediaStreamManager.acquire if needed
WebRTC.MediaHandler#getDescription: promisify mediaStreamManager.acquire if needed

This allows backward compatibility with callback-style MediaStreamManager implementations.

Escaux/SIP.js,onsip/SIP.js,josephfrazier/SIP.js,onsip/SIP.js,markandrus/SIP.js,joseph-onsip/SIP.js,ronlobo/SIP.js