GEODE-6180: Create unique results folder. (#23)

* Create unique results folder with timestamp if default output file is not set.
diff --git a/geode-benchmarks/build.gradle b/geode-benchmarks/build.gradle
index ee0fa09..d6469c6 100644
--- a/geode-benchmarks/build.gradle
+++ b/geode-benchmarks/build.gradle
@@ -24,9 +24,14 @@
 
 sourceCompatibility = 1.8
 
-def outputDir = project.hasProperty('outputDir') ? project.findProperty('outputDir') : new File(project.buildDir, "benchmarks").getAbsolutePath()
+def outputDir = project.hasProperty('outputDir') ? project.findProperty('outputDir') : new File(project.buildDir, "benchmarks_" + getDate()).getAbsolutePath()
 def geodeVersion = project.hasProperty('geodeVersion') ? project.findProperty('geodeVersion') : '1.+'
 
+def getDate() {
+    new Date().format('yyyyMMddHHmmss')
+}
+
+
 repositories {
     mavenCentral()
 }