acu161304 Fix up motd generation for trusty

Don't rely on rightimage script hijacking the motd.tail for us, on
Trusty this file seems to have been removed.
acu161304 - Merge branch 'ivory_14_12_acu161304_ubuntu_trusty' into ivory_14_12_acu161304_ubuntu_trusty_remix

* ivory_14_12_acu161304_ubuntu_trusty:
  acu161304 Add trusty to rightscale_software repo generator
Merge pull request #449 from rightscale/ivory_14_12_acu161304_ubuntu_trusty_remix

acu161304 Fix up motd generation for trusty