use the collection directly (#10917)

getComputers() calls getComputerCollection() before using streams to sort the entries, to put the results into an array, all just to get the number of computers.
just use the collection directly and call size() to avoid the overhead.

core/src/main/java/hudson/slaves/NodeProvisioner.java

@@ -251,7 +251,7 @@ public class NodeProvisioner {
                                 LOGGER.log(Level.INFO,
                                         "{0} provisioning successfully completed. "
                                                 + "We have now {1,number,integer} computer(s)",
-                                        new Object[]{f.displayName, jenkins.getComputers().length});
+                                        new Object[]{f.displayName, jenkins.getComputersCollection().size()});
                                 fireOnCommit(f, node);
                             } catch (IOException e) {
                                 LOGGER.log(Level.WARNING,