race condition appear when chain workflow execution run in short time

[Bo Tran]

Hi, every body.
I using mistral from git with branch master and had use cron triggers.
With a long time use cron triggers, i was noticed:

When i run a cron triggers with workflow execution have long time for execute and the interval time of cron triggers is shorter than workflow execution time was emit error log such as ".. trust not found..".

The steps to perform to emit error logs is:
1. Create a workflow such as list volumes, list servers, or something.
2. Create a cron trigger use the above workflow with pattern "* * * * *" (or can also is "* * * * *")

When this cron trigger run, we will being receive error log.

I was also know, my bug same this bug in here: https://bugs.launchpad.net/mistral/+bug/1708139.
But not work.
I hope this bug will be fixed.
Thanks