precise image prompts for update to trusty

[zyga]

While testing precise I found that it shows the annoying prompt just after booting and logging in.

A quick dconf inspection lead me to this:

vagrant@vagrant-ubuntu-precise-32:~$ dconf dump / > before
vagrant@vagrant-ubuntu-precise-32:~$ dconf dump / > after
vagrant@vagrant-ubuntu-precise-32:~$ diff -u before after 
--- before  2015-07-13 18:03:44.078263034 +0000
+++ after   2015-07-13 18:03:51.582509307 +0000
@@ -1,4 +1,5 @@
 [apps/update-manager]
+check-new-release-ignore='trusty'
 remind-reload=false

 [com/canonical/unity-2d]