LXC 3.0, unlike 2.1, doesn't support old configuration formats at all
and because our previous approach to handling old format was incomplete,
running `vagrant up` on a system with LXC 3.0 would fail, even if the
base box itself was made with modernized config.
This commit fixes this problem: is the box has a modern config, it's
going to be properly created and booted under LXC 3.0. It does so
without breaking the support for LXC < 2.1
To fix#406, I reverted the tmpfs mount we add at boot time. As we can
see in #455, it was a bad idea.
In addition to bringing back that mount, I've also added a
`tmpfs_mount_size` config that allows to change the size of the mount
from its default `2G`. It's also possible to disable the mount
altogether.
fixes#455
fixes#406 because the `tmpfs` mount isn't needed anymore.
Careful considerations had to be taken because #68 mentions host-side
data loss when cleaning up `/tmp`. We mitigate this by ensuring that all
mounts under `/tmp` are unmounted before we proceed with our `rm -rf`
operation.
More context about this issue can be found in #360.
Previously, the utsname of a machine was set to the vagrant machine ID.
As the utsname represents the hostname of the machine and is independent
from the name of the actual LXC container, the hostname that was
specified in the Vagrantfile should be used instead. If no hostname is
provided, the machine ID will be used like before.
Additionally, this will trigger the DHCP client in the container to send
the correct hostname to the DHCP server on the first request at boot.
Vagrant sets the configured hostname only after the network is up. If
for example automatic DNS updates are configured, the right DNS record
will be created every time.
