lxc-start-ephemeral: Allow unprivileged run

This allows running lxc-start-ephemeral using overlayfs. aufs remains
blocked as it hasn't been looked at and patched to work in the kernel at
this point (not sure if it ever wil).

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
travis: Drop workaround introduced last week

Travis has now corrected the bug in their build environment so we no
longer need to force the autogen script through bash.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>