OPC Simulator workaround (#142)

## Purpose
Temporarily set OPC simulator version to 2.12.39 until issue with 2.12.40 is addressed

## Does this introduce a breaking change?
<!-- Mark one with an "x". -->
```
[ ] Yes
[x] No
```

## Pull Request Type
What kind of change does this Pull Request introduce?

<!-- Please check the one that applies to this PR using "x". -->
```
[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:
```

Author: dominicbetts

samples/quickstarts/opc-plc-deployment.yaml

@@ -17,7 +17,7 @@ spec:
     spec:
       containers:
       - name: opc-plc
-        image: mcr.microsoft.com/iotedge/opc-plc:latest
+        image: mcr.microsoft.com/iotedge/opc-plc:2.12.39
         args:
           - "--ph=opcplc-000000"
           - "--cdn=opcplc-000000"

samples/quickstarts/opc-plc-tutorial-deployment.yaml

@@ -17,7 +17,7 @@ spec:
     spec:
       containers:
       - name: opc-plc
-        image: mcr.microsoft.com/iotedge/opc-plc:latest
+        image: mcr.microsoft.com/iotedge/opc-plc:2.12.39
         args:
           - "--plchostname=opcplc-000000"
           - "--portnum=50000"