Fix capabilities support.

[Random-Liu]

The capabilities in CRI and docker doesn't have the CAP_ prefix. However, we need to add it when generating the runtime spec.

With another ExecSync PR I'll send out soon, we can pass the capabilities cri validation test now:

# critest --runtime-endpoint=/var/run/cri-containerd.sock --focus=Capabili validation
Running Suite: E2ECRI Suite
===========================
Random Seed: 1497147284 - Will randomize all specs
Will run 1 of 36 specs

SSSSSSSSSSSSSSSSS
------------------------------
[k8s.io] Security Context runtime should support container with security context 
  runtime should support setting Capability
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:369
[BeforeEach] [k8s.io] Security Context
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/framework/framework.go:50
[BeforeEach] [k8s.io] Security Context
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:49
[It] runtime should support setting Capability
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:369
STEP: create pod
STEP: create container with security context Capability and test
STEP: create Capability container
STEP: Get image status for image: busybox:1.26
STEP: Pull image : busybox:1.26
STEP: Create container.
Jun 11 02:14:47.629: INFO: Created container "0f7d2fc7b86e3816c237819af959492b25f2ab39f81c222533e586b2ebfddd47"

STEP: Start container for containerID: 0f7d2fc7b86e3816c237819af959492b25f2ab39f81c222533e586b2ebfddd47
Jun 11 02:14:47.754: INFO: Started container "0f7d2fc7b86e3816c237819af959492b25f2ab39f81c222533e586b2ebfddd47"

STEP: Get container status for containerID: 0f7d2fc7b86e3816c237819af959492b25f2ab39f81c222533e586b2ebfddd47
STEP: create container without security context Capability and test
STEP: Get image status for image: busybox:1.26
STEP: Create container.
Jun 11 02:14:47.813: INFO: Created container "20abe0a3e304364ef0aeeb65cb617f1fda3dc82d4f322d0a592801ab415aeb52"

STEP: Start container for containerID: 20abe0a3e304364ef0aeeb65cb617f1fda3dc82d4f322d0a592801ab415aeb52
Jun 11 02:14:47.928: INFO: Started container "20abe0a3e304364ef0aeeb65cb617f1fda3dc82d4f322d0a592801ab415aeb52"

STEP: Get container status for containerID: 20abe0a3e304364ef0aeeb65cb617f1fda3dc82d4f322d0a592801ab415aeb52
[AfterEach] runtime should support container with security context
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/validate/security_context.go:235
STEP: stop PodSandbox
STEP: delete PodSandbox
[AfterEach] [k8s.io] Security Context
  /home/lantaol/workspace/src/github.com/kubernetes-incubator/cri-tools/pkg/framework/framework.go:51
•SSSSSSSSSSSSSSSSSS
Ran 1 of 36 Specs in 3.215 seconds
SUCCESS! -- 1 Passed | 0 Failed | 0 Pending | 35 Skipped PASS

Ginkgo ran 1 suite in 3.284995122s
Test Suite Passed

/cc @heartlock
Signed-off-by: Lantao Liu [email protected]

[mikebrow]

LGTM... nit a comment around line 471 explaining why the CAP_ needs to be added

[Random-Liu]

LGTM... nit a comment around line 471 explaining why the CAP_ needs to be added

Done.

Apply LGTM based on #71 (review).