os::attempt_reserve_memory_at() tries too hard

The os::attempt_reserve_memory_at() function on BSD, linux and Solaris all try a bit too hard. They first try to mmap memory at a given address. If that failed, rather than giving up as expected, it tries in a loop to mmap random memory (without address hints), and looks if it can from random address ranges cut out the requested address range. We should just fail instead.