Allow eager instantiation of the instrumentation library

[evantorrie]

Please use the template provided below, when reporting bugs:

Expected Behavior

When mockery is used for test mocks, I don't want to see warnings about all of nyc/istanbul's modules that are required appearing prior to the first test.

Observed Behavior

Some mocking libraries hook require and by default warn when there is a required
module which has not been explicitly registered, e.g. mockery.
It is standard procedure to call mockery.enable() in a unit test prior to
requiring the code under test since obviously you want the hooks to be in place at the time that the

With lazy instantiation of the instrumenter, all of the instrumenter
library's requires generate mockery warnings at test time.

Bonus Points! Code (or Repository) that Reproduces Issue

See https://gist.github.com/evantorrie/d702ccd2e0ac2f30deb76e336128bddd

[bcoe]

@evantorrie thanks for the thorough issue! hoping to have some time to dig into OSS this week, and will hopefully get to this. Would also happily accept a pull request.