Work towards improving rspec-support script support.

rspec-rails has been a little different than the other repos for a
while. As the shared script setups are improving rspec-rails should
evolve to leverage these as much as possible.

Copy current support function and clone scripts. Update the run build
script to leverage the new scripts. Along the same lines, tweak the
travis build to be more inline as well.
Include the travis retry wrapping in rake tasks.

Often rspec-rails has gem timeout issues when running the acceptance
suite. To help prevent the common build timeout failures, utilize the
`travis_retry` function to wrap the bundler install.
Adjust rubocop config for rspec-support.

Invert the Rubocop config file setup to be in-line with rspec-support
configurations. One more step closer to syncing shared rspec-support
configs in rspec-rails.
Customize build process.

Prep for rspec/rspec-dev#78:
- Move custom functions into dedicated file
- Update run_script to load custom functions
Hook build update to keep travis config.
Merge pull request #1144 from rspec/port-rspec-support-scripts

Port some of the rspec dev scripts