Add support for scheduler_tests in cmake

Summary: cmake doesn't set define about boost::this_thread::sleep_for and alike. This hasn't been an issue since Boost 1.52, but we are requiring Boost 1.58, so we don't really care.

Test Plan:

ninja
./src/test/test_bitcoin

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1245