Restructured node template testcases in file test_toscatplvalidation.py
Restructured node template testcases in file test_toscatplvalidation.py

Testcases for the _single_node_template_content_test method in
file test_toscatplvalidation.py have been implemented to
handle exception and checking error messages in calling the
method.

Change-Id: Ib5a5c608667dda4ca82d2540d5c5ca0d64ee9099
Closes-Bug: #1497955

openstack/tosca-parser,openstack/tosca-parser