[perftest] Add test for zx_nanosleep() using a range of sleep times

This acts as an example of a parameterized test. It's also useful in
its own right for measuring the overhead and variation of sleeping.

Add a convenience function for registering parameterized tests.

ZX-1715

Change-Id: I9f0b25e86e9488016d0783577bfa8ef980f848bc