Add tracking for exec session IDs

Exec sessions now have an ID generated and assigned to their PID
and stored in the database state. This allows us to track what
exec sessions are currently active.

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>

Closes: #412
Approved by: baude

libpod/container_inspect.go

@@ -20,6 +20,11 @@ func (c *Container) getContainerInspectData(size bool, driverData *inspect.Data)
 		args = args[1:]
 	}
 
+	execIDs := []string{}
+	for id, _ := range c.state.ExecSessions {
+		execIDs = append(execIDs, id)
+	}
+
 	data := &inspect.ContainerInspectData{
 		ID:      config.ID,
 		Created: config.CreatedTime,
@@ -50,7 +55,7 @@ func (c *Container) getContainerInspectData(size bool, driverData *inspect.Data)
 		MountLabel:      config.MountLabel,
 		ProcessLabel:    spec.Process.SelinuxLabel,
 		AppArmorProfile: spec.Process.ApparmorProfile,
-		ExecIDs:         []string{}, //TODO
+		ExecIDs:         execIDs,
 		GraphDriver:     driverData,
 		Mounts:          spec.Mounts,
 		NetworkSettings: &inspect.NetworkSettings{