Update commands.py

Resource processor - Re-instate az login and az acr login commands prior to porter explain command to fix microsoft#3950

resource_processor/resources/commands.py

@@ -104,8 +104,10 @@ async def build_porter_command_for_outputs(msg_body):
 
 
 async def get_porter_parameter_keys(config, msg_body):
-    command = [f"porter explain --reference {config['registry_server']}/{msg_body['name']}:v{msg_body['version']} --output json"]
-
+    command = [f"{azure_login_command(config)} && \
+        {azure_acr_login_command(config)} && \
+        porter explain --reference {config['registry_server']}/{msg_body['name']}:v{msg_body['version']} --output json"]
+
     proc = await asyncio.create_subprocess_shell(
         ''.join(command),
         stdout=asyncio.subprocess.PIPE,