Allow lxc driver to accept bind mount config similarly to the docker
driver.
Includes some static sanity checks in Validate step
Signed-off-by: Michael McCracken <mikmccra@cisco.com>
Ideally DriverNetwork would be fully populated in Driver.Prestart, but
Docker doesn't assign the container's IP until you start the container.
However, it's important to setup the port env vars before calling
Driver.Start, so Prestart should populate that.
Cleanup can be used for cleaning up resources created by drivers to run
a task. Initially the Docker driver is the only user (to remove
downloaded images).
The Driver.Prestart method currently does very little but lays the
foundation for where lifecycle plugins can interleave execution _after_
task environment setup but _before_ the task starts.
Currently Prestart does two things:
* Any driver specific task environment building
* Download Docker images
This change also attaches a TaskEvent emitter to Drivers, so they can
emit events during task initialization.
Since lxc support requires linking to a C lib at compile and runtime
I'm putting it behind a build flag to avoid forcing all nomad users to
install liblxc (lxc-dev for development).
Michael McCracken