Update configuration tests to handle ParseError (in addition to ExpatError)
allow python 2.7 in Travis CI
add add_to_path shell function in build.sh

requires 1 arg - new path,
add it to the PATH only once (script is called repetitively)
eg add_to_path /home/joe/nta/eng
export NUPIC_INSTALL addition to PATH

we use it to pip install,
but later tests failed when python was called without this addition.

This fixes the functionality
export pythonpath too
Specify python version in env.sh
ParseError not present in Python 2.6, workaround

see
https://bugs.launchpad.net/nova/+bug/893757
http://github.com/openstack/nova/commit/b6ae26ba279246d1b9e32b8665316a47847147ce
use other error type instead
Revert "add add_to_path shell function in build.sh"

This reverts commits touching build.sh,
as we discussed and dont want to change PATH.
$NTA is added to PYTHONPATH

instead of to PATH.
it must be added somewhere or some tests fail