vendor: udpate agent dependency

To include the grpc yamux dialer.

Included kata agent git shortlog:
Archana Shinde (1):
      mount: Correct error message with mount failure.

Eric Ernst (2):
      Merge pull request kata-containers#196 from sboeuf/fix_rollback
      Merge pull request kata-containers#201 from bergwolf/yamux_client

Graham whaley (1):
      ci: lib: allow override of tests_repo

James O. D. Hunt (16):
      mount: Log params and validate
      device: Add validation and debug
      tests: Move helper function
      tests: Use root skip function
      tests: Skip more tests if non-root
      CI: Require pullapprove ack for protocol changes
      agent: Add announce function
      announce: Add standard fields when running as PID 1
      announce: Add device and storage handlers
      announce: Add total memory
      Merge pull request kata-containers#180 from jodh-intel/add-announce-log-call
      github: Add issue template
      Merge pull request kata-containers#189 from grahamwhaley/20180322_tests_repo
      Merge pull request kata-containers#187 from jodh-intel/github-issue-template
      Merge pull request kata-containers#192 from sboeuf/fix_device
      Merge pull request kata-containers#197 from amshinde/correct-err-msg

Lai Jiangshan (1):
      Merge pull request kata-containers#176 from jodh-intel/pullapprove-for-grpc-changes

Peng Tao (3):
      Merge pull request kata-containers#171 from jodh-intel/validate-mount-params
      Merge pull request kata-containers#206 from sboeuf/fix_rollback
      protocol: client: enable builtin yamux client support

Sebastien Boeuf (7):
      Merge pull request kata-containers#178 from jodh-intel/skip-more-tests-if-not-root
      Merge pull request kata-containers#173 from jodh-intel/add-device-debug
      device: VmPath can be empty if an Id is provided
      agent: Rollback properly when container creation fails
      vendor: Update libcontainer vendoring
      Merge pull request kata-containers#203 from sboeuf/revendor_libcontainer
      agent: Fix container creation rollback

Signed-off-by: Peng Tao <bergwolf@gmail.com>

Gopkg.toml

@@ -60,7 +60,7 @@
 
 [[constraint]]
   name = "github.com/kata-containers/agent"
-  revision = "a93071539feee29bfa22b6184380d3fd7c156ef7"
+  revision = "c8199f60759a1d52932df37a1af710cdeada8c81"
 
 [[constraint]]
   name = "github.com/containerd/cri-containerd"
@@ -74,3 +74,7 @@
   non-go = true
   go-tests = true
   unused-packages = true
+
+[[constraint]]
+  branch = "master"
+  name = "github.com/hashicorp/yamux"