Add IdentifiedUser#getLoggableName()

Callers that want to include a unique identifier of an IdentifiedUser
into a log currently use getUserName() but this method may return null
which makes the log useless. Instead of letting every caller handle the
null case add a new getLoggableName() method to IdentifiedUser that is
guaranteed to return a unique name for the user. We can't offer this
method on CurrentUser level since CurrentUser has no access to the
account and a user name may not be set.

Change-Id: I79433c5e37f8d5186e281c2590578e0aecf85e71
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/server/git/receive/ReceiveCommits.java

@@ -918,7 +918,7 @@ class ReceiveCommits {
                 reject(cmd, "invalid project configuration");
                 logError(
                     "User "
-                        + user.getUserName()
+                        + user.getLoggableName()
                         + " tried to push invalid project configuration "
                         + cmd.getNewId().name()
                         + " for "
@@ -994,7 +994,7 @@ class ReceiveCommits {
               reject(cmd, "invalid project configuration");
               logError(
                   "User "
-                      + user.getUserName()
+                      + user.getLoggableName()
                       + " tried to push invalid project configuration "
                       + cmd.getNewId().name()
                       + " for "

java/com/google/gerrit/server/git/validators/CommitValidators.java

@@ -447,7 +447,7 @@ public class CommitValidators {
         } catch (ConfigInvalidException | IOException e) {
           log.error(
               "User "
-                  + user.getUserName()
+                  + user.getLoggableName()
                   + " tried to push an invalid project configuration "
                   + receiveEvent.command.getNewId().name()
                   + " for project "