Don't require 'turn' from rails/test_help

If 'turn' is in the Gemfile with `:require => nil`, Rails should
respect that.

This supports the case where 'turn' may or may not be required
depending on different developers' preference or environment. E.g., you
require turn for local testing, but not on your CI server by putting
this in `test/test_helper.rb`:

    require 'turn' if ENV['TURN']
Update guides/source/getting_started.md

Reflect change in 009873a that renamed the script/ folder to bin/
Merge pull request #8802 from claudiob/patch-1

Update guides/source/getting_started.md [ci skip]
Avoid Rack security warning no secret provided

This avoids "SECURITY WARNING: No secret option provided to Rack::Session::Cookie."
Merge pull request #8801 from ktheory/dont_require_turn

Don't require 'turn' from rails/test_help
Don't configure Turn output, we aren't using it since 3.2.0
change unless !blank? to if blank? in get_primary_key
Use absolute path

It is semantically correct than relative path.
Merge pull request #8808 from tricknotes/use-absolute-path

Use absolute path [ci skip]
Merge pull request #8800 from acapilleri/primary_key

refactor reset_primary_key and change !blank? to present? in get_primary...
Ignore binds payload with nil column in AR log subscriber

Some tests were raising the following error:

    Could not log "sql.active_record" event. NoMethodError: undefined method
    `type' for nil:NilClass`

Due to the way binds were being logged, the column info was considered
always present, but that is not true for some of the tests listed in the
issue.

Closes #8806.