Set HOME env var and proper perms on nodetool in Ubuntu

* The `service` command strips environmental variables, which
  casued issues with `erlexec` when it couldn't find $HOME.
  This fixes that issue: #135

* Ubuntu 12.04 had improper permissions set on nodetool, so this
  ensures it is executable by non-priviledged users at bootstrap.
  This fixes that issue: #136
Merge pull request #137 from basho/jem-service-strips-env

Set HOME env var and proper perms on nodetool in Ubuntu