Move rake task definition into #define.
Moved ivar initialization back into #initialize.
Merge pull request #1493 from postmodern/code_smell

Code smell
Set @rspec_path to the direct rspec script using Gem.bin_path.

* Ensures that we run the same version of rspec as what is already
  loaded.
* Bypasses rubygems binstubs and executes the rspec script directly.
* Still supports bundler binstubs.