Set submitWholeTopic field in ServerInfo only if it is not false

This is consistent with how the other boolean fields are treated.

Also add tests for this field.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Ib8afe7ec64a37f540ff59d73c7e6c4e9bc6d9aad
diff --git a/Documentation/rest-api-config.txt b/Documentation/rest-api-config.txt
index e757130..b58d22a 100644
--- a/Documentation/rest-api-config.txt
+++ b/Documentation/rest-api-config.txt
@@ -1545,7 +1545,7 @@
 |`update_delay`       ||
 link:config-gerrit.html#change.updateDelay[How often in seconds the web
 interface should poll for updates to the currently open change].
-|`submit_whole_topic` ||
+|`submit_whole_topic` |not set if `false`|
 link:config-gerrit.html#change.submitWholeTopic[A configuration if
 the whole topic is submitted].
 |`disable_private_changes` |not set if `false`|