Summary:
It looks like 20s might not be sufficient anymore as the test is failing too
frequently with `wait` completing without the process having completed:
```
eden/fs/service/test/StartupLoggerTest.cpp:352: Failure
Expected equality of these values:
"exited with status 0"
returnCode.str()
Which is: "running"
eden/fs/service/test/StartupLoggerTest.cpp:363: Failure
Value of: isWritablePipeBroken(fd)
Actual: false
Expected: true
```
Reviewed By: kmancini
Differential Revision: D29342002
fbshipit-source-id: d457b632a2666356e9053d2da66a3227e6524b68
b73322e5ea