Skip Bundler and Rubygems while executing ruby scripts in cukes

Speeds up subprocess execution by preparing the LOAD_PATH for nested
interpreter invocations. Some attempt to do this existed previously but
it wasn't efficent and did rely on Rubygems nevertheless.

Bundler is only used for subprocesses that need to invoke gem binstubs
such as `cucumber` and `rspec`. Such cukes are tagged "@with-bundler".
Speed up cukes by having Aruba wait less for IO

The default was 100 ms. Leave that default for JRuby.

Seems like 5 seconds isn't enough on CI:
https://travis-ci.org/vcr/vcr/jobs/37566372

Ruby 2.0.0 fails pretty consistently if timeout is around 10s or less:
https://travis-ci.org/vcr/vcr/jobs/37569992

Of course, I have no idea why.
Avoid Cucumber deprecation notice
Tweak local server for testing
Randomize test server ports in cukes

Previously, cukes typically used ports 7777 and 8888 for spinning up the
Sinatra test server. This would fail when the user already has something
running on one of these ports, like Charles proxy which typically runs
on 8888.

Now the ports are randomized and picked based on availability. This also
means that there is no chance of port collisions in the condition when
one subprocess is shutting down a server while the other is starting a
new one.
Don't fail the CI build if simplecov segfaulted. It happens often
Compatibility with Ruby 1.8 and Rubygems 1.6
Add `script/test` for running individual files/directories
Enable Travis folds in CI output
Output timing information per test operation in Travis web interface
Bring back Redcarpet for YARD

This out it's necessary for building docs after all.