Sleep after unsubscribing and enable validation for unsubscribe test.

There is a possibility that the disconnect happened too quickly after
unsubscribe, thus not allowing a clean unsubscribe and broker queuing
messages for that client even after disconnect.

tests/keywords.txt

@@ -48,5 +48,6 @@
 | | Connect     | ${broker.uri} | ${broker.port}    | ${client.id}  | ${false}
 | | @{messages} | Subscribe     | ${topic} | ${qos} | ${timeout}    | ${limit}
 | | Unsubscribe | ${topic}
+| | Sleep       | 1s
 | | [Teardown]  | Disconnect
 | | [Return]    | @{messages}

tests/pubsub.txt

@@ -127,4 +127,4 @@
 | | Publish to MQTT Broker and Disconnect   | topic=${topic}    | message=test message2 | qos=1
 | | @{messages} | Subscribe and Get Messages    | client.id=${client}   | topic=${topic}
 | | LOG         | ${messages}
-#| | Length Should Be            | ${messages}       | 0
+| | Length Should Be            | ${messages}       | 0