Agents running on OpenJDK does not collect CPU stats
#### Description
`CpuLoadMetricSetSelector` currently returns `EmptyCpuLoadMetricSet` when running on open jdk. Since open jdk can use the same cpu load collector as the one used on oracle jvm, adding a simple check should fix this problem - related to #2330

#### Environment
<!--- Include as many relevant details about the environment you experienced the bug in -->
* Pinpoint version: 1.6.0
* OS, WAS, affected library, etc: Affects agents running on OpenJDK vm
* Additional details (e.g. how your collector/web is set up): not applicable

profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java
profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java
diff --git a/profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java b/profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java
index c3f841fde9c0..8111cb620b40 100644
--- a/profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java
+++ b/profiler/src/main/java/com/navercorp/pinpoint/profiler/monitor/codahale/cpu/CpuLoadMetricSetSelector.java
@@ -52,7 +52,7 @@ public static CpuLoadMetricSet getCpuLoadMetricSet(String vendorName) {
             vmType = JvmUtils.getType();
         }
         JvmVersion vmVersion = JvmUtils.getVersion();
-        if (vmType == JvmType.ORACLE) {
+        if (vmType == JvmType.ORACLE || vmType == JvmType.OPENJDK) {
             if (vmVersion.onOrAfter(JvmVersion.JAVA_7)) {
                 classToLoad = ORACLE_CPU_LOAD_METRIC_SET_FQCN;
             } else if (vmVersion.onOrAfter(JvmVersion.JAVA_5)) {
