Fix race in module fork kill test (#10717)

The purpose of the test is to kill the child while it is running.
From the last two lines we can see the child exits before being killed.
```
- Module fork started pid: 56998
* <fork> fork child started
- Killing running module fork child: 56998
* <fork> fork child exiting
signal-handler (1652267501) Received SIGUSR1 in child, exiting now.
```

In this commit, we pass an argument to `fork.create` indicating how
long it should sleep. For the fork kill test, we use a longer time to
avoid the child exiting before being killed.

Other changes:
use wait_for_condition instead of hardcoded `after 250`.
Unify the test for failing fork with the one for killing it (save time) 

0 files changed, 0 insertions, 0 deletions