Extend sleep/timeout for ngoroutine check

In cases where this is failing it's ok to have the test take extra time,
but we don't want it to fail because of some race/performance
differences between systems.
So make the timeout go to 30s and double the sleep time in between
checks so it's not pounding the daemon quite so fast.

Originally I couldn't make this test fail (pre-change), but changed
graphdrivers and saw a failure pretty quickly.
This change seems to smooth that out.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>