rename mustrunas to capabilities

The file context has nothing to do with `mustrunas`, so it's quite
odd to use `mustrunas` as the file name. I guess it's copied from other
places.

pkg/security/podsecuritypolicy/capabilities/BUILD

@@ -9,8 +9,8 @@ load(
 go_library(
     name = "go_default_library",
     srcs = [
+        "capabilities.go",
         "doc.go",
-        "mustrunas.go",
         "types.go",
     ],
     importpath = "k8s.io/kubernetes/pkg/security/podsecuritypolicy/capabilities",
@@ -24,7 +24,7 @@ go_library(
 
 go_test(
     name = "go_default_test",
-    srcs = ["mustrunas_test.go"],
+    srcs = ["capabilities_test.go"],
     importpath = "k8s.io/kubernetes/pkg/security/podsecuritypolicy/capabilities",
     library = ":go_default_library",
     deps = [