Fix MaxCpuUsage placement strategy NPE

Author: grkvlt

docker/src/main/java/brooklyn/location/docker/strategy/MaxCpuUsagePlacementStrategy.java

@@ -20,6 +20,7 @@
 
 import brooklyn.config.ConfigKey;
 import brooklyn.entity.basic.ConfigKeys;
+import brooklyn.entity.basic.SoftwareProcess;
 import brooklyn.entity.container.docker.DockerHost;
 import brooklyn.entity.container.docker.DockerInfrastructure;
 import brooklyn.location.docker.DockerHostLocation;
@@ -52,7 +53,10 @@ public boolean apply(DockerHostLocation input) {
         }
         if (maxCpu == null) maxCpu = DEFAULT_MAX_CPU_USAGE;
 
+        Boolean serviceUp = input.getOwner().getAttribute(SoftwareProcess.SERVICE_UP);
         Double currentCpu = input.getOwner().getAttribute(DockerHost.CPU_USAGE);
+        if (!Boolean.TRUE.equals(serviceUp) || currentCpu == null) return false; // reject
+
         boolean accept = currentCpu < maxCpu;
         if (LOG.isDebugEnabled()) {
             LOG.debug("Location {} CPU usage is {}: {}", new Object[] { input, currentCpu, accept ? "accepted" : "rejected" });