Removing the gembag and the download of the vendored files since the logic was moved into their specific gems.

Fixes #2272
Update for windows to execute rake bootstrap and bin\logstash.bat

Fixes #2085
allow implicit agent using directly a flag in cli

Fixes #1296
add a generic spec helper where all logstash specs referre to and where they can get for example helper classes that makes running test easier
upgrade rspec to 2.99, prior to be upgraded to final 3.0 branch
change the current example reference to the customary rspec 3 way
Upgraded it to rspec 3.1.x, start the first style refactoring within the
conditionals_spec to make them more clear and disabled the json_spec (to
be enabled later) as it was interfering with others.

Added also a generic spec_helper where the helper classes should be
living.
add more operators specs
make the config spec more rspec alike
Made the event_spec more RSpec 3 friendly, using the time to also get
rid of insist, reject, and companions.
ammend previous commit
Add an option throw LOGSTASH_TEST=true to use the documentation
formatter as an rspec formatter as it helps while debugging.
ammend rspec import
divert the configuration using the documentation format within the test case, so all deps are installed
put the rspec into the spec helper