add apt_proxy support

cloudinit/CloudConfig/cc_apt_update_upgrade.py

@@ -39,6 +39,20 @@ def handle(name,cfg,cloud,log,args):
             "archive.ubuntu.com/ubuntu")
         rename_apt_lists(old_mir, mirror)
 
+
+    # set up proxy
+    proxy = cfg.get("apt_proxy", None)
+    proxy_filename = "/etc/apt/apt.conf.d/95cloud-init-proxy"
+    if proxy:
+        try:
+            contents = "Acquire::HTTP::Proxy:: \"%s\";\n"
+            with open(proxy_filename,"w") as fp:
+                fp.write(contents % proxy)
+        except Exception as e:
+            log.warn("Failed to write proxy to %s" % proxy_filename)
+    elif os.path.isfile(proxy_filename):
+        os.unlink(proxy_filename)
+
     # process 'apt_sources'
     if cfg.has_key('apt_sources'):
         errors = add_sources(cfg['apt_sources'],