sleep after creating source thread

Sometimes the source thread does not start immediately.
This fix seems to help.
3 jobs for 158 in 6 minutes and 16 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Configure
passed #34637
linux
configure-linux

00:00:14

 
  Compile
failed #34638
linux
make-linux

00:06:01

 
  Unit Test
skipped #34639
linux
test
 
Name Stage Failure
failed
make-linux Compile
make[2]: *** Waiting for unfinished jobs....
CMakeFiles/Makefile2:565: recipe for target 'CMakeFiles/core.dir/all' failed
make[1]: *** [CMakeFiles/core.dir/all] Error 2
make: *** [all] Error 2
Makefile:160: recipe for target 'all' failed
Running after script...
$ echo "End CI"
End CI
ERROR: Job failed: exit code 1