Ubuntu Touch session manager

Merge proposals dependent on lp://staging/~xavi-garcia-mena/ubuntu-touch-session/bug-1317860-env-variable-poweroff

  1. bug-1317860-env-variable-poweroff
  2. Dependent merge proposals

lp://staging/~xavi-garcia-mena/ubuntu-touch-session/bug-1317860-env-variable-poweroff has no merge proposals.