Fix closing connected RevPiSlaveDev on program exit.

RevPiSlaveDev are daemon threads and we have to .join() after calling .stop()
to let the thread finish its work of disconnect and write default values to
process image.

.idea/misc.xml

@@ -3,7 +3,7 @@
   <component name="JavaScriptSettings">
     <option name="languageLevel" value="ES6" />
   </component>
-  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.6 (revpi)" project-jdk-type="Python SDK" />
+  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.8 (revpi)" project-jdk-type="Python SDK" />
   <component name="PythonCompatibilityInspectionAdvertiser">
     <option name="version" value="3" />
   </component>

.idea/revpipyload.iml

@@ -5,7 +5,7 @@
       <sourceFolder url="file://$MODULE_DIR$/revpipyload" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/lib" isTestSource="false" />
     </content>
-    <orderEntry type="jdk" jdkName="Python 3.6 (revpi)" jdkType="Python SDK" />
+    <orderEntry type="jdk" jdkName="Python 3.8 (revpi)" jdkType="Python SDK" />
     <orderEntry type="sourceFolder" forTests="false" />
   </component>
 </module>