testrunner: Add NOSE_COLOR env var

Allows forcing output of color to non terminal.

Useful for case where the errors are longer then the scrollback:

    NOSE_COLOR=1 ./run_tests_local.sh jsonRpcTests | less -R

Change-Id: I4eb684c73f6254a35707fcd7f3f6b30eaaae9f2f
Signed-off-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/12302
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>