add c->may_control

This is an api function which will return false if the container
is running, and the caller may not talk to its monitor over its
command socket.  Otherwise - if the container is not running, or
the caller may access it - it returns true.

We can use this in several tools early on to prevent the segvs
etc which we currently get.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>