Allow the container to share the PID namespace with the host

We want to be able to use container without the PID namespace.  We basically
want containers that can manage the host os, which I call Super Privileged
Containers.  We eventually would like to get to the point where the only
namespace we use is the MNT namespace to bring the Apps userspace with it.

By eliminating the PID namespace we can get better communication between the
host and the clients and potentially tools like strace and gdb become easier
to use.  We also see tools like libvirtd running within a container telling
systemd to place a VM in a particular cgroup, we need to have communications of the PID.

I don't see us needing to share PID namespaces between containers, since this
is really what docker exec does.

So currently I see us just needing docker run --pid=host

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)