Add support for container kernel capabilities (#716)

This patch adds two new command-line flags to specify one or
more kernel capabilities to add or remove from the workflow
containers.

The command-line flag `--container-cap-add` allows for adding
specific capabilities on the workflow containers; where as,

The command-line flag `--container-cap-drop` allows for removing
specific capabilities on the workflow containers.

This was developed to specifically be able to add `SYS_PTRACE`
to a workflow I maintain. It involves using this capability to
monitor a make build, to then build a compilation database.

Signed-off-by: Joseph Benden <joe@benden.us>

pkg/runner/step_context.go

@@ -299,7 +299,7 @@ func (sc *StepContext) runUsesContainer() common.Executor {
 		return common.NewPipelineExecutor(
 			stepContainer.Pull(rc.Config.ForcePull),
 			stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
-			stepContainer.Create(),
+			stepContainer.Create(rc.Config.ContainerCapAdd, rc.Config.ContainerCapDrop),
 			stepContainer.Start(true),
 		).Finally(
 			stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
@@ -517,7 +517,7 @@ func (sc *StepContext) execAsDocker(ctx context.Context, action *model.Action, a
 		prepImage,
 		stepContainer.Pull(rc.Config.ForcePull),
 		stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),
-		stepContainer.Create(),
+		stepContainer.Create(rc.Config.ContainerCapAdd, rc.Config.ContainerCapDrop),
 		stepContainer.Start(true),
 	).Finally(
 		stepContainer.Remove().IfBool(!rc.Config.ReuseContainers),