Fix multistrap issue when building iso on Ubuntu 14.04

In case Ubuntu 14.04:
- we add presice repository with low priority
- install multistrap version 2.1.6 from precise repo which
has higher priority over trusty one
For all distribution:
- nodejs from chris-lea repository has higher priority and
will be (re)installed
- fixed npm global installation permission issue

Change-Id: I62ba9257fb3d575d996bf4c57b5d983c0050fd3b
Closes-Bug: #1337343
Closes-Bug: #1312654