Replace easy_install resource with python_package

[jeffbyrnes]

Adds a dependency on poise-python.

Fixes #539

Relates to #541

[olivielpeau]

I'd like to avoid adding a dependency on a new cookbook in order to only provide this recipe:

• maintaining cookbook dependencies/version constraints over time is always a bit tricky (for example see all the "recommendation" notes in metadata.rb and in the README), and
• I feel the use case of installing the ddtrace pip package could be more easily addressed by documenting it in the README

Instead, I'd prefer deprecating the ddtrace-python recipe in datadog 2.17 , and remove it in 3.0 (while documenting how to use poise-python to achieve the same purpose). What do you think?

[jeffbyrnes]

@olivielpeau I think that’s reasonable! I think it’s probably out-of-scope for me to tackle a deprecation in a cookbook I don’t maintain directly, so I’ll close this & leave that to you.