Improve neutron CLI existing tests

Objective of this patch to parse the output of read only neutron CLI's, 
to validate the output and improve more output verification.
It is improving the code of all below read only neutron CLI's sub-commands:
1. net-list
2. net-external-list
3. port-list
4. router-list
5. security-group-rule-list
6. subnet-list

Partially implements: blueprint missing-cli-tests-in-tempest

Task is managed using etherpad :
https://etherpad.openstack.org/p/missing-cli-tests-in-tempest)

Change-Id: I9b8c9cd0ab115a08519c0d2474c41836a984cce2
diff --git a/tempest/cli/simple_read_only/test_neutron.py b/tempest/cli/simple_read_only/test_neutron.py
index c1d58b5..49d079e 100644
--- a/tempest/cli/simple_read_only/test_neutron.py
+++ b/tempest/cli/simple_read_only/test_neutron.py
@@ -49,7 +49,8 @@
 
     @test.attr(type='smoke')
     def test_neutron_net_list(self):
-        self.neutron('net-list')
+        net_list = self.parser.listing(self.neutron('net-list'))
+        self.assertTableStruct(net_list, ['id', 'name', 'subnets'])
 
     @test.attr(type='smoke')
     def test_neutron_ext_list(self):
@@ -111,11 +112,14 @@
     @test.attr(type='smoke')
     @test.requires_ext(extension='external-net', service='network')
     def test_neutron_net_external_list(self):
-        self.neutron('net-external-list')
+        net_ext_list = self.parser.listing(self.neutron('net-external-list'))
+        self.assertTableStruct(net_ext_list, ['id', 'name', 'subnets'])
 
     @test.attr(type='smoke')
     def test_neutron_port_list(self):
-        self.neutron('port-list')
+        port_list = self.parser.listing(self.neutron('port-list'))
+        self.assertTableStruct(port_list, ['id', 'name', 'mac_address',
+                                           'fixed_ips'])
 
     @test.attr(type='smoke')
     @test.requires_ext(extension='quotas', service='network')
@@ -125,7 +129,9 @@
     @test.attr(type='smoke')
     @test.requires_ext(extension='router', service='network')
     def test_neutron_router_list(self):
-        self.neutron('router-list')
+        router_list = self.parser.listing(self.neutron('router-list'))
+        self.assertTableStruct(router_list, ['id', 'name',
+                                             'external_gateway_info'])
 
     @test.attr(type='smoke')
     @test.requires_ext(extension='security-group', service='network')
@@ -136,11 +142,18 @@
     @test.attr(type='smoke')
     @test.requires_ext(extension='security-group', service='network')
     def test_neutron_security_group_rule_list(self):
-        self.neutron('security-group-rule-list')
+        security_grp = self.parser.listing(self.neutron
+                                           ('security-group-rule-list'))
+        self.assertTableStruct(security_grp, ['id', 'security_group',
+                                              'direction', 'protocol',
+                                              'remote_ip_prefix',
+                                              'remote_group'])
 
     @test.attr(type='smoke')
     def test_neutron_subnet_list(self):
-        self.neutron('subnet-list')
+        subnet_list = self.parser.listing(self.neutron('subnet-list'))
+        self.assertTableStruct(subnet_list, ['id', 'name', 'cidr',
+                                             'allocation_pools'])
 
     @test.attr(type='smoke')
     def test_neutron_help(self):