Default use_proxy to True for fetch_url()

Also added some error handling to the fetch_url() call in the
apt_repository module, so that failures to look up the PPA info
are properly handled.

Fixes #7322

lib/ansible/module_utils/urls.py

@@ -207,7 +207,7 @@ def url_argument_spec():
 
 
 def fetch_url(module, url, data=None, headers=None, method=None, 
-              use_proxy=False, force=False, last_mod_time=None, timeout=10):
+              use_proxy=True, force=False, last_mod_time=None, timeout=10):
     '''
     Fetches a file from an HTTP/FTP server using urllib2
     '''

library/packaging/apt_repository

@@ -320,6 +320,8 @@ class UbuntuSourcesList(SourcesList):
 
         headers = dict(Accept='application/json')
         response, info = fetch_url(self.module, lp_api, headers=headers)
+        if info['status'] != 200:
+            self.module.fail_json(msg="failed to fetch PPA information, error was: %s" % info['msg'])
         return json.load(response)
 
     def _expand_ppa(self, path):