The guava library of the target platform is to old. I get this error when I try to use influxdb.ping().

```
!MESSAGE com.google.common.base.Stopwatch.createStarted()Lcom/google/common/base/Stopwatch;
!STACK 0
java.lang.NoSuchMethodError: com.google.common.base.Stopwatch.createStarted()Lcom/google/common/base/Stopwatch;
	at org.influxdb.impl.InfluxDBImpl.ping(InfluxDBImpl.java:76)
	at org.openhab.persistence.influxdb.internal.InfluxDBPersistenceService.connect(InfluxDBPersistenceService.java:95)
	at org.openhab.persistence.influxdb.internal.InfluxDBPersistenceService.updated(InfluxDBPersistenceService.java:199)
	at org.eclipse.equinox.internal.cm.ManagedServiceTracker$1.run(ManagedServiceTracker.java:183)
	at org.eclipse.equinox.internal.cm.SerializedTaskQueue$1.run(SerializedTaskQueue.java:36)
```

Stopwatch.createStarted seems to be available since guava 15.0 the target platform provides 10.0.
I could add a guava jar to the plugin. What do you think?