Sergey,

This patch refactors the <lang/coroutine.lua> test by adding a simple
check for the content of a `debug.traceback()` result. Also, the test is
moved to the <lib/coroutine/> directory.

Also, it removes the <misc/coro_traceback.lua> since it is the same test
that wasn't cleaned up during the refactoring in the original
repository.

Part of tarantool/tarantool#9398
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thanks for the patch! LGTM

Please add a note to the top of the file that test is fragile

and depends on a number of lines in the file.