In particular, only create /dev/console when it is set to "none".
Otherwise, we will bind mount a pts device later, so let's just leave it.

Also, when bind mounting the pts device, let's create /dev/console if it
doesn't exist, since it may not already exist due to the above :)

v2: s/ot/to
v3: add O_EXCL so we actually get EEXIST, use the right condition for
    mount_console (we want to compare against console.path, not
    console.name, and console.path can be null)
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>