fix: ReadableStream detection in Chrome Apps

Detection via `stream instanceof Stream` does not work correctly in browser context,
especially when different polyfils are used and mixed together.

This change replaces instanceof check with feature-detection of stream-like objects.
It enables Hapi to be used in Chrome Apps (browser environments with additional chrome.sockets APIs)

Real life example:
ipfs/ipfs-companion#664

lib/response.js

@@ -98,7 +98,7 @@ exports = module.exports = internals.Response = class {
             this.variety = 'buffer';
             this._contentType = 'application/octet-stream';
         }
-        else if (source instanceof Stream) {
+        else if (Streams.isReadableStream(source)) {
             this.variety = 'stream';
             this._contentType = 'application/octet-stream';
         }
@@ -529,7 +529,7 @@ exports = module.exports = internals.Response = class {
 
         // Stream source
 
-        if (source instanceof Stream) {
+        if (Streams.isStream(source)) {
             if (typeof source._read !== 'function') {
                 throw Boom.badImplementation('Stream must have a readable interface');
             }
@@ -607,7 +607,7 @@ exports = module.exports = internals.Response = class {
         }
 
         const stream = this._payload || this.source;
-        if (stream instanceof Stream) {
+        if (Streams.isReadableStream(stream)) {
             internals.Response.drain(stream);
         }
     }

lib/streams.js

@@ -7,6 +7,20 @@ const internals = {
     team: Symbol('team')
 };
 
+exports.isStream = function (stream) {
+
+    return stream !== null &&
+    typeof stream === 'object' &&
+    typeof stream.pipe === 'function';
+};
+
+exports.isReadableStream = function (stream) {
+
+    return exports.isStream(stream) &&
+    stream.readable !== false &&
+    typeof stream._read === 'function' &&
+    typeof stream._readableState === 'object';
+};
 
 exports.drain = function (stream) {