Refactor of _check_tenant_network_connectivity

This is to make the following changes of _check_tenant_network_
connectivity:
1. remove the leading underscore in opencos_base._check_tenant_
   network_connectivity for it's not an internal helper.
2. remove the helper with same name _check_tenant_network_
   connectivity in TestNetworkBasicOps, which unnecessary adds
   the hierachy depth.

Change-Id: Iaced16610f39ebb0efc822b25cda519794a846f3
3 files changed