Fix presto tests, add to CI, update integration details

[ericmustin]

This PR adds Presto Tests to the CI properly this time, as well as add a fix and tests for analytics, and lastly addresses an issue where the ensure block not having an implicit return was causing some specs to fail.

According to rubygems the min ruby version here for presto-client is 1.9.1 (see below), so I've gone back through the rake tasks and ensured that presto tests run for all versions currently supported.

• versioning note while the listed min version is 1.9.1, originally the 2.0 specs were failing. I looked into this and in 0.5.13 they added the usage of Process::CLOCK_MONOTONIC (changelog) which is only supported in >=ruby2.1. They've removed support for 2.0 and lower (commit), and given that dd-trace-rb only supports presto-client >= 0.5.14 , I've removed the presto tests from all ruby 2.0 related tests in the ci, rakefile, and docker-compose

Additionally, it looks like some last minute tinkering with variable names for datadog_configuration was creating some issues with setting span tags, as the analytics sampling block was throwing an error which caused the span's resource name not to get set properly. This has been fixed, not sure how that slipped through my development testing, but was compounded by the fact that the presto tests weren't added to the circleci config properly.

I believe I added the mock presto container to the circleci config properly but making this PR should validate or surface any issues, as it's a bit hard to test this locally.

Thanks for the patience here

[marcotc]

🎆 Great work @ericmustin, thank you for the quick turnaround on this follow up PR.