openposix: Fix generate-makefiles and speculative tests.

After the change that included dirname in test binary names the
testcases in foo/speculative/ directories became
"speculative_x-y.run-test". This commit adds special case to the
makefile generator so that they end up as foo_speculative_x-y.run-test
instead.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>