Further EVPN changes for JUNOS interop.

Fix bug in parsing of Sequence to get PMSI Tunnel atrribute to work.
Add integration tests with 2 BgpServers to bgp_xmpp_evpn_test.cc.
Merge pull request #13 from Juniper/evpn-devel

Sync with evpn-devel.
Merge pull request #14 from Juniper/nsheth-evpn-devel

Nsheth evpn devel