dockerinit: create a long-running dockerinit

Create a long-running dockerinit which does some setup, starts the
container app, waits for it to finish, and exits with the app's exit
code.

A long-running dockerinit is a prerequisite for using libvirt-lxc, since
libvirt provides no way to return an exit code, and no way to split
stdout and stderr into separate streams.

It also will allow docker to get rid of the ugly Ghost state, and might
even make it possible to do everything in the docker client and get rid
of the docker daemon altogether.
dockerinit: reap zombies
dockerinit: forward signals

Forward all signals received by dockerinit to the app, so that
dockerinit behaves more like the app itself.
dockerinit: add RPC socket and Resume call

Create a per-container UNIX socket which is used for RPC communication
between the docker daemon and dockerinit.  The socket file is stored in
a bind-mounted directory, seen as /.dockersocket/rpc.sock within the
container.

Also add a Resume() RPC call which will allow docker to pause the
container startup until it's ready to resume.  This will be used in the
future to allow docker to hook up the console before resuming the
container so it doesn't miss any output.  The Resume() call will also be
needed for exit code reporting.
fix rpc file descriptor leak

Work around a bug in the Go RPC Client Close() function which returns an
error when the connection has already been closed, but doesn't close the
underlying socket FD.

https://code.google.com/p/go/issues/detail?id=6897
dockerinit: exit code reporting

Add dockerinit RPC Wait() function that waits for the container app to
exit and returns its exit code to the docker daemon.

This is needed for using libvirt-lxc because libvirt doesn't provide the
exit code.  It will also help docker get rid of the Ghost state.
dockerinit: kill support
dockerinit: import rpcfd package

Import Alex Larsson's rpcfd package from:

  https://github.com/alexlarsson/fdrpc

It will be used by dockerinit to pass the console FDs over the RPC
socket.
dockerinit: console FD passing

Move all the pty/pipe console handling into dockerinit.  Use the rpcfd
package to pass the console FDs to the docker daemon.

This will allow us to get rid of the container Ghost state, since the
docker daemon can always reconnect to the container's console if needed.
It will also enable stdin/stdout/stderr separation when using
libvirt-lxc.
dockerinit: unmount socket directory
dockerinit: goodbye Ghost state

Now that we can always reconnect to dockerinit to connect to the console
and wait for the exit code, the Ghost state can go bye bye.
dockerinit: machine container support

Detect when the app is a "machine container" with its own init process.
In this case, since upstart and systemd require running as PID 1, the
original dockerinit will have to "fork" a child long-running dockerinit
before exec-ing the real init.
remove pid from container state

Don't store the pid since nobody is using it.
container: make Start asynchronous again

Remove the code in Start that makes sure the container is really running
before returning.  It's quite hackish and unnecessary.  With the
dockerinit code and the rpc/pty locks there should hopefully not be any
race conditions in the start path.
test: get rid of LXC-specific tests

Since we're moving to a container plugin infrastructure, these tests
don't currently work with the LXC plugin and they'll never work with the
libvirt plugin.
test: make TestEnv non lxc-specific
lxc: create lxc container plugin

Create a container plugin infrastructure and move the lxc-specific code
to its own plugin.
network: create dockernet plugin

Create a network plugin infrastructure and move the bridge creation code
to a new "dockernet" plugin.
dockerinit: privileged device cgroup access

When using libvirt-lxc in privileged mode, enable cgroup device access
from dockerinit, since libvirt doesn't support it.
libvirt: create libvirt-lxc plugins

Create container and network plugins for libvirt-lxc.  If libvirtd is
running, use the libvirt plugins.  Otherwise use the dockernet and lxc
plugins.

With this change, docker must be dynamically linked since libvirt
doesn't seem to support being statically linked, based on the compile
errors seen.