Fix compatibility with ansible 1.6.7 and above.

Since ansible 1.6.7 it is no longer allowed to insert parameters in
module args (check
https://groups.google.com/forum/#!topic/ansible-announce/RGEEMmFaqBQ
and CVE-2014-4967) As such, the tasks for adding node to the PATH
and the update-alternatives execution had to be changed.
Also, the alternatives modules is now used for executing the
update-alternatives.
Updated ansible to 1.7 in travis ci.
Travis build failing after changing to 1.7, testing 1.6.9.
Revert to original travis badge link for PR. [ci skip]