Fix test_keepalived_ipv6_support for Keepalived v1.2.20

In commit [1] (some explanation in [2] ) VRRP initialisation is enhanced
to read source IP address(to use when sending VRRP packets) from the
HA interface or from keepalived config("unicast_src_ip" parameter).
If it is unable to find IP address, VRRP initialisation will fail with
error "Cannot find an IP address to use for interface".

In the test, we set vrrp->family to AF_INET by setting vip to
169.254.0.1/24 through config, but not providing source IPv4 address(i.e
no 'unicast_src_ip' option or no IP on HA interface), making the test
to fail with [1]. To fix that, we set the IP address on HA interface.

Note: Commit [1] is added in Keepalived version 1.2.20.
Tested the fix on both Keepalived v1.2.19 and Keepalived v1.2.20.

[1] https://github.com/acassen/keepalived/commit/37488e57
[2] https://github.com/acassen/keepalived/issues/445

Closes-bug: #1712388
Change-Id: I260c0e6810ed54c93f93621afa6ab13855ef2428

neutron/cmd/sanity/checks.py

@@ -340,6 +340,7 @@ def keepalived_ipv6_supported():
 
             ha_dev.link.set_up()
             gw_dev.link.set_up()
+            ha_dev.addr.add('169.254.192.8/18')
 
             ka.configure()