Do not drop sys_boot

This fixes #2391
Utils: Add ShellQuoteArguments
lxc: Work around lxc-start need for private mounts

lxc-start requires / to be mounted private, otherwise the changes
it does inside the container (both mounts and unmounts) will propagate
out to the host.

We work around this by starting up lxc-start in its own namespace where
we set / to rshared.

Unfortunately go can't really execute any code between clone and exec,
so we can't do this in a nice way. Instead we have a horrible hack that
use the unshare command, the shell and the mount command...
- Fix the attach examples according to the new attach behavior
- Add the option of adding the user to docker's group and avoid the usage of "sudo" before each command
- Included the sudo alternative as an example_header
Add warning about SYS_BOOT capability with pre-3.4 kernels and pre-0.8 LXC.
Add more depth to the upstart example in host_integration.rst

I found that the original example wasn't starting the docker container when docker is started.  So, I modified it using information I found from https://groups.google.com/forum/#!msg/docker-user/OWz8EOpiXuo/L_uxGFQuYlkJ

Also, upstart wasn't starting docker if it wasn't running ahead of time.  So, I added a change to the docker upstart script to solve this.
Clean up sphinx syntax, upgrade http markup package, minor link changes, update intro.
Improvise documentation for builder.rst / VOLUME command
thankyou @tomdz - I forgot about URL based ADDs
Move integration tests to integration/, expose missing public methods in the core
Integration tests: remove dependency on private APIs
gofmt
Remove deprecated tags_test.go
Merge pull request #2691 from SvenDowideit/add-instruction-path-limitations

except URL-based ADDs
Merge pull request #2445 from alexlarsson/fix-shared-root-from-dm

Fix lxc start for shared root filesystems
fix Integration tests
move TestMount to integration
Fix the brittle errorstring-to-httperror recognition code which in turn is required by autopull (the client issues a pull if container creation returns 404)
Merge pull request #2704 from shykes/fix-auto-pull

Fix the brittle errorstring-to-httperror recognition code