Add createVectorOf helper function
Allow passing multiple triggers to Proactor::expect

After this commit, Proactor::expect is a member function template that
can accept any number of trigger arguments.

Some test helper functions in AwaiterTestHelper.hh are removed in favor
of the new Proactor::expect.
Move timeout-unrelated tests to AwaiterTest
Work around GCC bug in createVectorOf

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51253
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61382