Update network context in selected rally tests

Update network context in selected rally tests

Network context not needed in following scenarios:

NeutronNetworks.create_and_delete_routers
NeutronNetworks.create_and_list_routers
NeutronNetworks.create_and_list_subnets
NeutronNetworks.create_and_update_routers
NeutronNetworks.create_and_update_subnets
NeutronNetworks.create_and_show_routers

Router not needed in network context in following scenarios:

NeutronNetworks.create_and_update_ports
NeutronNetworks.create_and_delete_ports
NeutronNetworks.create_and_delete_subnets
NeutronNetworks.create_and_list_ports
NeutronNetworks.create_and_show_ports
NeutronNetworks.create_and_show_subnets

This completes the patch skipping router creation [1].

[1] https://gerrit.opnfv.org/gerrit/#/c/67429/

Change-Id: I80ea145a21168fd984cc9ef88d50af227f0d6ed4
Signed-off-by: Juha Kosonen <juha.kosonen@nokia.com>
(cherry picked from commit b4b2e7f9a5a3cb3379b45ac4ddd0ef949974a698)