locking: update per Dwight's comment

Create three pairs of functions:
	int process_lock(void);
	void process_unlock(void);
	int container_mem_lock(struct lxc_container *c)
	void container_mem_unlock(struct lxc_container *c)
	int container_disk_lock(struct lxc_container *c);
	void container_disk_unlock(struct lxc_container *c);

and use those in lxccontainer.c

process_lock() is to protect the process state among multiple threads.
container_mem_lock() is to protect a struct container among multiple
threads.  container_disk_lock is to protect a container on disk.

Also remove the lock in lxcapi_init_pid() as Dwight suggested.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>