config: repair installer for 17.1-BETA

The installer user is injected for install media login, but
we authenticate against our database now instead.  This has
larger consequences that require a persistent installer user,
which is not so easy to disable/defang after installation.

Hopefully this is temporary.

src/etc/config.xml.sample

@@ -229,6 +229,7 @@
     </bogons>
     <kill_states/>
     <backupcount>60</backupcount>
+    <disableintegratedauth>1</disableintegratedauth>
   </system>
   <interfaces>
     <wan>