server: improve stats collector logs to state what the collector does (#8387)

This simply improves the log statement that prints debug statements
during beginning of a stats collector run for hosts or VMs.

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

Author: yadvr

server/src/main/java/com/cloud/server/StatsCollector.java

@@ -644,13 +644,12 @@ class HostCollector extends AbstractStatsCollector {
         @Override
         protected void runInContext() {
             try {
-                LOGGER.debug("HostStatsCollector is running...");
-
                 SearchCriteria<HostVO> sc = createSearchCriteriaForHostTypeRoutingStateUpAndNotInMaintenance();
-
-                Map<Object, Object> metrics = new HashMap<>();
                 List<HostVO> hosts = _hostDao.search(sc, null);
 
+                LOGGER.debug(String.format("HostStatsCollector is running to process %d UP hosts", hosts.size()));
+
+                Map<Object, Object> metrics = new HashMap<>();
                 for (HostVO host : hosts) {
                     HostStatsEntry hostStatsEntry = (HostStatsEntry) _resourceMgr.getHostStatistics(host.getId());
                     if (hostStatsEntry != null) {
@@ -1192,13 +1191,12 @@ class VmStatsCollector extends AbstractStatsCollector {
         @Override
         protected void runInContext() {
             try {
-                LOGGER.trace("VmStatsCollector is running...");
-
                 SearchCriteria<HostVO> sc = createSearchCriteriaForHostTypeRoutingStateUpAndNotInMaintenance();
                 List<HostVO> hosts = _hostDao.search(sc, null);
 
-                Map<Object, Object> metrics = new HashMap<>();
+                LOGGER.debug(String.format("VmStatsCollector is running to process VMs across %d UP hosts", hosts.size()));
 
+                Map<Object, Object> metrics = new HashMap<>();
                 for (HostVO host : hosts) {
                     Date timestamp = new Date();
                     Map<Long, VMInstanceVO> vmMap = getVmMapForStatsForHost(host);