Contract with releng/builder parts of CSIT: define and verify

releng/builder contains bash scripts that do initial environment preparation before starting integration/test Robot suites. But it is not always clear what state of ODL (or environment) should the suites assume.

For example, currently the scrips guarantee GET to restconf/modules results in status code 200. But some suites use netconf-connector, which may or may not be ready at that point. And if it is not ready, it is not clear whether suites should wait patiently, or whether they should fail.

Check_Whether_Netconf_Connector_Works test case of "netconfready" suite reports immediate failure, citing this Bug as the reason.
The next test case Wait_For_Netconf_Connector than waits patiently, allowing subsequent suites to assume netconf-connector is ready.

For more background, see comments in https://git.opendaylight.org/gerrit/26446