Add and change lttcomm socket API

Add lttcomm_alloc_sock_from_uri(), lttcomm_destroy_sock(),
lttcomm_alloc_copy_sock() and lttcomm_copy_sock(). Also add the relayd
command and lttcomm error message.

Change the create and alloc sock call API arguments.

Fix the fd leak in accept() function.

Signed-off-by: David Goulet <dgoulet@efficios.com>