ARI: Allow specifying channel variables during a POST /channels

Added the ability to specify channel variables when creating/originating a
channel in ARI.  The variables are sent in the body of the request and should
be formatted as a single level JSON object.  No nested objects allowed.
For example: {"variable1": "foo", "variable2": "bar"}.

(closes issue ASTERISK-22872)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/3052/
........

Merged revisions 403752 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403757 65c4cc65-6c06-0410-ace0-fbb531ad65f3

rest-api/api-docs/channels.json

@@ -88,6 +88,14 @@
 							"allowMultiple": false,
 							"dataType": "int",
 							"defaultValue": 30
+						},
+						{
+							"name": "variables",
+							"description": "Variables to be set on the channel.",
+							"paramType": "body",
+							"required": false,
+							"allowMultiple": false,
+							"dataType": "containers"
 						}
 					],
 					"errorResponses": [