MT#8195 use dst_leg peer id and lookup against peer group/contract ID

Squashed commit of the following:

commit e137454f9d871332ef055b3de8eb9c703caece03
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Jul 25 11:03:17 2014 -0400

    MT#8195 lookup peer host ID against peer group/contract ID

commit 47e3509e634d9892fc1e2bc8111df6a90416addc
Author: Richard Fuchs <rfuchs@sipwise.com>
Date:   Fri Jul 18 11:03:23 2014 -0400

    MT#8195 use dst_leg peer id