Core handling of TTLs (#4230)

* govet cleanup in token store

* adding general ttl handling to login requests

* consolidating TTL calculation to system view

* deprecate LeaseExtend

* deprecate LeaseExtend

* set the increment to the correct value

* move calculateTTL out of SystemView

* remove unused value

* add back clearing of lease id

* implement core ttl in some backends

* removing increment and issue time from lease options

* adding ttl tests, fixing some compile issue

* adding ttl tests

* fixing some explicit max TTL logic

* fixing up some tests

* removing unneeded test

* off by one errors...

* adding back some logic for bc

* adding period to return on renewal

* tweaking max ttl capping slightly

* use the appropriate precision for ttl calculation

* deprecate proto fields instead of delete

* addressing feedback

* moving TTL handling for backends to core

* mongo is a secret backend not auth

* adding estimated ttl for backends that also manage the expiration time

* set the estimate values before calling the renew request

* moving calculate TTL to framework, revert removal of increment and issue time from logical

* minor edits

* addressing feedback

* address more feedback

audit/hashstructure_test.go

@@ -19,8 +19,7 @@ func TestCopy_auth(t *testing.T) {
 	// Make a non-pointer one so that it can't be modified directly
 	expected := logical.Auth{
 		LeaseOptions: logical.LeaseOptions{
-			TTL:       1 * time.Hour,
-			IssueTime: time.Now(),
+			TTL: 1 * time.Hour,
 		},
 
 		ClientToken: "foo",
@@ -183,16 +182,14 @@ func TestHash(t *testing.T) {
 		{
 			&logical.Auth{
 				LeaseOptions: logical.LeaseOptions{
-					TTL:       1 * time.Hour,
-					IssueTime: now,
+					TTL: 1 * time.Hour,
 				},
 
 				ClientToken: "foo",
 			},
 			&logical.Auth{
 				LeaseOptions: logical.LeaseOptions{
-					TTL:       1 * time.Hour,
-					IssueTime: now,
+					TTL: 1 * time.Hour,
 				},
 
 				ClientToken: "hmac-sha256:08ba357e274f528065766c770a639abf6809b39ccfd37c2a3157c7f51954da0a",