Update Raft Vendoring

[mkeeler]

Pulls in a fix for a potential memory leak regarding consistent reads that invoke VerifyLeader.

This is the comparison for our current version to the update (useful if you want the commit message context)
hashicorp/raft@6d14f0c...master

[mkeeler]

Before these changes and after letting a cluster run for a while with constant kv write + consistent read:

(pprof) top5
Showing nodes accounting for 10920.40kB, 95.52% of 11432.45kB total
Showing top 5 nodes out of 51
      flat  flat%   sum%        cum   cum%
 5120.43kB 44.79% 44.79%  5120.43kB 44.79%  github.com/hashicorp/consul/vendor/github.com/hashicorp/raft.(*Raft).VerifyLeader /go/src/github.com/hashicorp/consul/vendor/github.com/hashicorp/raft/future.go
 4096.25kB 35.83% 80.62%  4096.25kB 35.83%  github.com/hashicorp/consul/vendor/github.com/hashicorp/raft.(*Raft).VerifyLeader /go/src/github.com/hashicorp/consul/vendor/github.com/hashicorp/raft/api.go
  678.95kB  5.94% 86.56%   678.95kB  5.94%  github.com/hashicorp/consul/vendor/github.com/hashicorp/raft.(*Raft).verifyLeader /go/src/github.com/hashicorp/consul/vendor/github.com/hashicorp/raft/raft.go
  512.69kB  4.48% 91.04%   512.69kB  4.48%  crypto/x509.parseCertificate /usr/local/go/src/crypto/x509/x509.go
  512.08kB  4.48% 95.52%   512.08kB  4.48%  net/http.(*Server).Serve /usr/local/go/src/net/http/server.go

After the changes:

(pprof) top5
Showing nodes accounting for 2703.62kB, 56.89% of 4752.21kB total
Showing top 5 nodes out of 67
      flat  flat%   sum%        cum   cum%
  591.75kB 12.45% 12.45%   591.75kB 12.45%  crypto/elliptic.initTable /usr/local/go/src/crypto/elliptic/p256_amd64.go
  544.67kB 11.46% 23.91%   544.67kB 11.46%  github.com/hashicorp/consul/vendor/github.com/hashicorp/memberlist.(*NetTransport).udpListen /go/src/github.com/hashicorp/consul/vendor/github.com/hashicorp/memberlist/net_transport.go
  540.51kB 11.37% 35.29%   540.51kB 11.37%  github.com/hashicorp/consul/agent.New /go/src/github.com/hashicorp/consul/agent/agent.go
     514kB 10.82% 46.10%      514kB 10.82%  github.com/hashicorp/consul/vendor/github.com/hashicorp/serf/serf.Create /go/src/github.com/hashicorp/consul/vendor/github.com/hashicorp/serf/serf/serf.go
  512.69kB 10.79% 56.89%  1024.97kB 21.57%  crypto/x509.parseCertificate /usr/local/go/src/crypto/x509/x509.go

One other difference is that during the first run I was executing against the HTTP API on the leader server whereas in the second run I happened to be using an other client. That accounts for why the crypto/x509.parseCertificate and net/http Serve are not in the second pprof output.

[banks]

Cool!