Better worker restarts

[jnogol]

Prerequisites

• Put an X between the brackets on this line if you have done all of the following:
  • Checked that your issue isn't already filled: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aidealista
  • Checked that there is not already provided the described functionality

Description

At the moment, when the workers are restarted, they do so the work they're performing is interrupted. Following this Stackoverflow answer provided by @juanriaza, the workers can be gracefully restarted by sending them SIGINT kill signal.