Add missing methods to NoopFirewallDriver

The fix adds missing methods into generic Firewall class
and in NoopFirewall driver class.

Change-Id: I6402448075ed414434dc007f5c403fc85b6b1456
Closes-Bug: #1369685
Related-Bug: #1365806
(cherry picked from commit 9a6c073656a7e0b1a26b2bca0ba381489d04e322)
Raise exception if ipv6 prefix is inappropriate for address mode

Address prefix to use with slaac and stateless ipv6 address modes
should be equal to 64 in order to work properly.
The patch adds corresponding validation and fixes unit tests
accordingly.

Change-Id: I6c344b21a69f85f2885a72377171f70309b26775
Closes-Bug: #1357084
(cherry picked from commit 0d8911115e1b722da2f1e92f444e53b22223ee32)
Allow reading a tenant router's external IP

Adds an external IPs field to the external gateway information
for a router so the external IP address of the router can be
read by the tenant.

DocImpact

Closes-Bug: #1255142
Change-Id: If4e77c445e9b855ff77deea6c8df4a0b3cf249d4
(cherry picked from commit c7baaa068ed1d3c8b02717232edef60ba1b655f6)
Merge "Add missing methods to NoopFirewallDriver" into proposed/juno
Merge "Raise exception if ipv6 prefix is inappropriate for address mode" into proposed/juno
Merge "Allow reading a tenant router's external IP" into proposed/juno