conpaas: fixed inconsistencies between node.id and node.vmid.
conpaas: added a generic POST argument checker to be used by method decorated with expose('POST'), and with its unit tests.
conpaas: use BaseManager constants.
conpaas doc: updated the manifest guide with the commands to run to create an application from a manifest and to generate a manifest from an application.
conpaas: optional arguments description is optional.
conpaas: added primitives for expecting state ending with error if wrong state or waiting for the expecting state.
conpaas: skip pylint error as a quick workaround of a bad class design.
conpaas: enable pep8 and pylint checks for the webservers service. Fixing bugs found by pylint.
conpaas unit tests: make travis.sh call the conpaas-services unit-tests.sh script. Fixed some errors raised by pylint in webservers manager.