Fix the GOMAXPROCS warning for Upstart-based systems

Improvements to the Upstart startup script:

  * Set default value of GOMAXPROCS=2
  * Make GOMAXPROCS configurable via "/etc/default/consul"
  * Follow Upstart idioms like using setuid/setgid
Revert setuid/setgid Upstart changes which are incompatible with Ubuntu 10.04

Use `exec sudo ...` instead of Upstart's setuid/setgid directives
as those directives are not supported on older versions on Ubuntu.
Fix a few broken acceptance tests
Merge pull request #39 from tehranian/fix-upstart-conf

Fix the GOMAXPROCS warning for Upstart-based systems