defining an extra_daemon into an mfdata plugin avoids nominal stop of plugin step with SIGTERM

[matthieumarrast]

1. Switch to mfdata and start it.

su - mfdata
mfdata.start

2. Make a test plugin with command: bootstrap_plugin.py create test --no-input
cd test

3. Update plugin's config.ini by adding an extra_daemon:

[extra_daemon_test]
_cmd_and_args = ./test.sh
numprocesses=1
graceful_timeout = 30
rlimit_as = 1000000000
rlimit_nofile = 1000
rlimit_stack = 10000000
rlimit_fsize = 100000000
log_split_stdout_stderr=AUTO
log_split_multiple_workers=AUTO
max_age=0

3. Add an executable script test.sh in plugin's dir:

#!/bin/bash
wait_100s () {
    i=1
    while [ $i -le 100 ]
    do
        echo $i
        sleep 1
        i=$((i+1))
    done
}

cleanup() {
    echo "Signal SIGTERM received..."
    echo "Waiting (100s) more than graceful timeout (60s)"
    wait_100s
    echo "End of sleep after SIGTERM"
    exit 0
}

trap cleanup SIGTERM

echo "-----------------"
echo "start test script"
wait_100s
echo "end test script"
exit 0

chmod +x test.sh

4. Install plugin with make develop
   (step and extra_daemon will be launched by circus worker)

5. Try to stop plugin (with command mfdata.stop or plugins.stop never mind):
   plugins.stop test

[mfdata:~/test] $ plugins.stop test
- Collecting infos about plugins...                        [ OK ]              
- Scheduling stop of plugin: test
    - Scheduling stop of extra.test.test                   [ OK ]  
    - Scheduling stop of step.test.main                    [ ERROR ]    (???)
- Waiting for stop of plugin: test
    - Waiting for stop of extra.test.test...               [ OK ]    (it will be 'OK' after 30 seconds)
    - Waiting for stop of step.test.main...                [ RUNNING] 00:09:59

=> BUG: scheduling of the step ends with error and stop is waiting for 10 minutes, as per step timeout settings (600s)
=> if no extra daemon defined step is stopped immediately, without errors -> OK
=> if extra_daemon does not stop after SIGTERM it well waits for 60 seconds before stopping (SIGKILL) -> OK
=> note: command circustl stop step.test.main does not raise any problem