TeamCity: select latest patch version of go for mac builds (#2363)

Also adds a disabled tip builder for the next-version support branch.

_scripts/latestver.py

@@ -0,0 +1,11 @@
+#!/usr/bin/python
+import json
+import urllib
+import sys
+
+ver = sys.argv[1]
+d = json.loads(urllib.urlopen('https://golang.org/dl/?mode=json&include=all').read())
+for x in d:
+	if x['version'][:len(ver)] == ver:
+		print x['version']
+		exit(0)