Rename NeutronScenarioTest to NetworkScenarioTest

NetworkScenarioTest was temporarily renamed to NeutronScenarioTest
during the migration of scenario tests to tempest clients.
Now that the migration is complete, restore the original name.

Change-Id: If3e2612c8e971295f94ea422a17faf385cabb5c7
Partially-implements: bp/tempest-client-scenarios
Merge "Rename NeutronScenarioTest to NetworkScenarioTest"