Draft: Reduce sleeping in tests

Two weeks ago we discussed with @bourtemb the problem of sleeps/waits in test suites.

I'd like to trigger a discussion (in PR, just to show some code) - whether we shall focus (or not) on the problem and how can we improve our tests.

I've done a simple PoC of an event callback that maintains event queue and allows to perform assertions on received events. When applied to dev_intr_event testcase, execution time went down from ~11s to ~2s.

Pros:

• test suite execution time reduction -> faster CI feedback
• simpler test code (calback's state is reduced), no need to track cb_executed, etc.
• we can safely increase timeout value for cases where current sleep period is sometimes too low (unstable testcases) -> CI stability improvement

Cons:

• may hide some bugs when blindly applied to all sleep statements (see discussion in #524 (closed))

It's C++11 only, but I think with enough patience it can be rewritten to pthreads (lambdas will be a problem). Maybe we can start introducing C++11 first in test code (as there is little end-user impact).

Long running testcases:

• 100.09 CXX::cxx_reconnection_zmq
• 55.07 CXX::cxx_stateless_subscription
• 49.28 CXX::cxx_old_poll
• 44.21 CXX::cxx_poll_admin
• 40.12 event::multi_dev_event
• 38.66 old_tests::lock
• 38.18 CXX::cxx_fwd_att
• 32.08 asyn::asyn_write_cb
• 32.07 asyn::asyn_attr_cb
• 31.21 event::change_event
• 30.10 asyn::asyn_attr
• 30.07 asyn::asyn_write_attr
• 29.17 event::per_event
• 29.07 asyn::asyn_write_attr_multi
• 29.07 asyn::asyn_cb_cmd
• 29.07 asyn::asyn_attr_multi
• 28.26 event::att_type_event
• 27.07 asyn::asyn_cmd
• 26.12 event::archive_event
• 24.03 asyn::auto_asyn_cmd
• 23.13 event::change_event_buffer
• 23.12 event::multi_event
• 21.09 CXX::cxx_server_event
• 20.05 CXX::cxx_asyn_reconnection
• 13.06 asyn::asyn_cb2
• 13.03 asyn::asyn_cb
• 12.29 event::att_conf_event_buffer
• 12.16 old_tests::att_conf
• 11.31 old_tests::ring_depth
• 11.11 event::state_event
• 11.11 event::data_ready_event_buffer
• 11.10 event::dev_intr_event
• 11.09 event::change_event64
• 10.20 CXX::cxx_attr_misc
• 9.79 old_tests::state_attr
• 9.07 CXX::cxx_dserver_misc
• 8.07 CXX::cxx_enum_att
• 8.07 CXX::cxx_blackbox
• 8.04 CXX::cxx_signal
• 7.07 event::pipe_event
• 6.07 event::event_lock
• 6.04 CXX::cxx_attr_write
• 5.20 old_tests::rds
• 5.07 old_tests::attr_proxy
• 4.34 old_tests::attr_conf_test
• 4.05 CXX::cxx_class_dev_signal
• 4.04 CXX::cxx_class_signal
• 4.03 old_tests::sub_dev
• 3.55 old_tests::mem_att
• 3.08 CXX::cxx_misc
• 3.05 CXX::cxx_poll
• 2.07 event::user_event
• 2.06 old_tests::ConfEventBugClient
• 2.06 event::data_ready_event
• 2.03 event::att_conf_event
• 1.07 CXX::cxx_pipe_conf