Add connectivity test via 2 routers and tenant networks

This patch adds test to check if connectivity through 2 routers
and internal network between routers works fine.

When at least two compute nodes are available for tempest and
DifferentHostFilter is enabled in nova-scheduler VM1 and VM2 will be
spawned on two different compute nodes.

Connectivity scenario in test is like on picture below:

	    +-----+
	    | VM 1|
	    +--+--+
	       |
	       | Network 1 (tenant network)
	       |
	     +-+-+
	     | R1|
	     +-+-+
	       |
	       | Network 3 (tenant network)
	       |
	     +-+-+
	     | R2|
	     +-+-+
	       |
	       | Network 2 (tenant network)
	       |
	    +--+--+
	    | VM 2|
	    +-----+

Depends-On: https://review.openstack.org/597567
Change-Id: Ie9903b7078d6fcff307c5d76770d92df1152d473
Related-Bug: #1786272
3 files changed