[GEODE-5] Add Gradle version check and fail if not using minimum Grad…

…le version.

Tested by running build with Gradle 2.2.1, which fails, and with Gradle wrapper, which runs successfully.
Reviewed by: AMB

settings.gradle

@@ -8,3 +8,8 @@ include 'gemfire-core'
 include 'gemfire-web'
 include 'gemfire-web-api'
 include 'gemfire-assembly'
+
+def minimumGradleVersion = '2.3'
+if (GradleVersion.current() < GradleVersion.version(minimumGradleVersion)) {
+  throw new GradleException('Running with unsupported Gradle Version. Use Gradle Wrapper or with Gradle version >= ' + minimumGradleVersion)
+}