Improve Apache error message when run with insufficient privileges (#7129)

* fixes #6369

* Add changelog entry.

* Improve error message again.

CHANGELOG.md

@@ -10,7 +10,8 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
-*
+* The error message when Certbot's Apache plugin is unable to modify your
+  Apache configuration has been improved.
 
 ### Fixed
 
@@ -20,7 +21,7 @@ Despite us having broken lockstep, we are continuing to release new versions of
 all Certbot components during releases for the time being, however, the only
 package with changes other than its version number was:
 
-*
+* certbot-apache
 
 More details about these changes can be found on our GitHub repo.
 

certbot-apache/certbot_apache/configurator.py

@@ -276,7 +276,10 @@ class ApacheConfigurator(augeas_configurator.AugeasConfigurator):
             util.lock_dir_until_exit(self.option("server_root"))
         except (OSError, errors.LockError):
             logger.debug("Encountered error:", exc_info=True)
-            raise errors.PluginError("Unable to lock {0}".format(self.option("server_root")))
+            raise errors.PluginError(
+                "Unable to create a lock file in {0}. Are you running"
+                " Certbot with sufficient privileges to modify your"
+                " Apache configuration?".format(self.option("server_root")))
         self._prepared = True
 
     def _verify_exe_availability(self, exe):