lxc-attach: make sure exit status of command is returned
lxc-attach: make sure exit status of command is returned

Commit ae68cad763d5b39a6a9e51de2acd1ad128b720ca introduced a regression that
makes lxc-attach ignore the exit status of the executed command. This was first
identified in 3.0.4 LTS, while it worked on 3.0.3.

  # lxc-attach --version
  3.0.4
  # lxc-attach -n test false; echo $?
  0

Signed-off-by: Antonio Terceiro <9e4dabace4bf3e60d3d713b56a1c8e7e285b5f80@debian.org>
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=934983

hallyn/lxc,hallyn/lxc,hallyn/lxc