Increase Gerrit startup timeout to 300 seconds

The default is now 90 seconds and we run into that and timeout which
confuses systemd. To avoid confusing systemd increase the timeout to its
old value of 300 seconds which worked back with older Gerrit. Hopefully
this doesn't confuse systemd anymore.

Change-Id: I8476c832f950e18035e11f225202eff8572f5ce8

templates/gerrit.config.erb

@@ -52,6 +52,7 @@
 	includeDiff = <%= @sendemail_include_diff %>
 [container]
 	user = gerrit2
+	startupTimeout = 300
 <% if @java_home != "" -%>
 	javaHome = <%= @java_home %>
 <% end -%>