enable to run on ruby 1.8.7 (el6)

* Enforce ruby 1.8.7 hashrocket style and update via:
  `bundle exec rubocop --only='Style/HashSyntax' -a`

* Handle differences in net/http codebase between 1.8 and 1.9+

* On ruby 1.8, use posix-spawn in test harness

  > The posix-spawn library aims to implement a subset of the Ruby
  > 1.9 Process::spawn interface in a way that takes advantage of
  > fast process spawning interfaces when available and provides
  > sane fallbacks on systems that do not.

* Exclude rubocop and coco in bundle on ruby 1.8 to
  avoid pulling in deps like celluloid and rainbow.
gitignore downloaded etcd tarball and bin dir
resolve rubocop config changes in latest version

Resolves:

    AllCops/Includes was renamed to AllCops/Include

    Warning: Deprecated pattern style 'lib/**' in .rubocop.yml.
    Change to 'lib/**/*'
resolve rubocop failures in latest version