[Merge] lp:~jamesodhunt/upstart/setenv+getenv into lp:upstart

[James Hunt]

As discussed with Stéphane and Dmitrijs, added --global option (along with --job and --instance) which is currently a dummy but will soon be required to manipulate the Session Inits (or PID 1's) job environment table. The behaviour will therefore be as follows.

When run from the command-line:

# Implicitly modify global table
$ initctl set-env foo=bar

# Explicitly modify global table
initctl set-env --global foo=bar

# Explicitly modify job-local table
initctl set-env --job foo [ --instance "" ] foo=bar

... but when run from a job:

# Implicitly modify job-local table (reads UPSTART_JOB and UPSTART_INSTANCE).
initctl set-env foo=bar

# Explicitly modify job-local table
initctl set-env --job $UPSTART_JOB --instance $UPSTART_INSTANCE foo=bar

# Explicitly modify global table
initctl set-env --global foo=bar

-- 
https://code.launchpad.net/~jamesodhunt/upstart/setenv+getenv/+merge/142939
Your team Upstart Reviewers is requested to review the proposed merge of lp:~jamesodhunt/upstart/setenv+getenv into lp:upstart.