kerberos_service_tier -> service_identity
kerberos_service_tier -> service_identity

Summary:
This flag is used to pin a service to a certain key. For example, if the host has the following keys on it:
sys.dev/dev1506.prn1...   and
myidentity/dev1506.prn1...

By default, the service will accept communication on either of these identities. If you set kerberos_service_tier, it will only accept connections on the specified identity.

Since we already introduced the service_identity flag for picking out which ACL to use, let's reuse the same flag for this purpose.

By default we don't want to pin though, so I'm also introducing a -pin_service_identity flag.

Test Plan:
Added LOG(INFO) calls in ThriftServer, made sure we pin at the right times.

Made sure the ACL picking code still works as expected.

Reviewed By: acampi@fb.com

Subscribers: trunkagent, fbcode-common-diffs@, davejwatson, andrewcox, alandau, bmatheny, mhorowitz, mshneer, wstefancik

FB internal diff: D1729728

Signature: t1:1729728:1418201966:2925622bc9e84d3950fd52065ade0af69018c12f

LinusU/fbthrift,raphaelamorim/fbthrift,SergeyMakarenko/fbthrift,LinusU/fbthrift,facebook/fbthrift,sinjar666/fbthrift,kangkot/fbthrift,soumith/fbthrift,LinusU/fbthrift,maxwell-demon/fbthrift,chjp2046/fbthrift,kangkot/fbthrift,getyourguide/fbthrift,soumith/fbthrift,raphaelamorim/fbthrift,HankFaan/fbthrift,HankFaan/fbthrift,soumith/fbthrift,sinjar666/fbthrift,kangkot/fbthrift,maxwell-demon/fbthrift,jesboat/fbthrift,getyourguide/fbthrift,jesboat/fbthrift,kangkot/fbthrift,getyourguide/fbthrift,facebook/fbthrift,project-zerus/fbthrift,kangkot/fbthrift,jesboat/fbthrift,maxwell-demon/fbthrift,sinjar666/fbthrift,Orvid/fbthrift,maxwell-demon/fbthrift,project-zerus/fbthrift,getyourguide/fbthrift,Orvid/fbthrift,facebook/fbthrift,maxwell-demon/fbthrift,project-zerus/fbthrift,jesboat/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,getyourguide/fbthrift,SergeyMakarenko/fbthrift,HankFaan/fbthrift,uber/fbthrift,guker/fbthrift,guker/fbthrift,chjp2046/fbthrift,HankFaan/fbthrift,HankFaan/fbthrift,jesboat/fbthrift,Orvid/fbthrift,soumith/fbthrift,uber/fbthrift,facebook/fbthrift,raphaelamorim/fbthrift,uber/fbthrift,facebook/fbthrift,guker/fbthrift,uber/fbthrift,fengshao0907/fbthrift,Orvid/fbthrift,HankFaan/fbthrift,maxwell-demon/fbthrift,sinjar666/fbthrift,kangkot/fbthrift,SergeyMakarenko/fbthrift,maxwell-demon/fbthrift,maxwell-demon/fbthrift,chjp2046/fbthrift,fengshao0907/fbthrift,Orvid/fbthrift,uber/fbthrift,Orvid/fbthrift,project-zerus/fbthrift,uber/fbthrift,maxwell-demon/fbthrift,sinjar666/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,sinjar666/fbthrift,guker/fbthrift,HankFaan/fbthrift,HankFaan/fbthrift,project-zerus/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,fengshao0907/fbthrift,project-zerus/fbthrift,Orvid/fbthrift,getyourguide/fbthrift,fengshao0907/fbthrift,Orvid/fbthrift,facebook/fbthrift,project-zerus/fbthrift,raphaelamorim/fbthrift,jesboat/fbthrift,guker/fbthrift,raphaelamorim/fbthrift,LinusU/fbthrift,chjp2046/fbthrift,soumith/fbthrift,raphaelamorim/fbthrift,guker/fbthrift,fengshao0907/fbthrift,LinusU/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,LinusU/fbthrift,HankFaan/fbthrift,chjp2046/fbthrift,uber/fbthrift,kangkot/fbthrift,sinjar666/fbthrift,sinjar666/fbthrift,LinusU/fbthrift,Orvid/fbthrift,LinusU/fbthrift,kangkot/fbthrift,project-zerus/fbthrift,maxwell-demon/fbthrift,fengshao0907/fbthrift,soumith/fbthrift,chjp2046/fbthrift,soumith/fbthrift,getyourguide/fbthrift,facebook/fbthrift,facebook/fbthrift,HankFaan/fbthrift,project-zerus/fbthrift,jesboat/fbthrift,raphaelamorim/fbthrift,sinjar666/fbthrift,jesboat/fbthrift,LinusU/fbthrift,raphaelamorim/fbthrift,uber/fbthrift,jesboat/fbthrift,jesboat/fbthrift,project-zerus/fbthrift,soumith/fbthrift,LinusU/fbthrift,getyourguide/fbthrift,project-zerus/fbthrift,kangkot/fbthrift,raphaelamorim/fbthrift,guker/fbthrift,uber/fbthrift,getyourguide/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,uber/fbthrift,soumith/fbthrift,kangkot/fbthrift,chjp2046/fbthrift,maxwell-demon/fbthrift,sinjar666/fbthrift,Orvid/fbthrift,guker/fbthrift,chjp2046/fbthrift,SergeyMakarenko/fbthrift,getyourguide/fbthrift,guker/fbthrift,fengshao0907/fbthrift,facebook/fbthrift,raphaelamorim/fbthrift,chjp2046/fbthrift,project-zerus/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,fengshao0907/fbthrift,jesboat/fbthrift,kangkot/fbthrift,soumith/fbthrift,fengshao0907/fbthrift,SergeyMakarenko/fbthrift,chjp2046/fbthrift,uber/fbthrift,jesboat/fbthrift,raphaelamorim/fbthrift,SergeyMakarenko/fbthrift,guker/fbthrift,soumith/fbthrift,SergeyMakarenko/fbthrift,SergeyMakarenko/fbthrift,chjp2046/fbthrift,guker/fbthrift,getyourguide/fbthrift