Fix RegionUtils.initSDKRegions

RegionUtils.initSDKRegions tries to load the /etc/regions.xml file in the classpath using a leading /, which does not work with ClassLoader.getResourceAsStream (returns null)

The proposed fix uses the sorter solution RegionUtils.class.getResourceAsStream("/etc/regions.xml"), but would also work if the leading slash was removed : classLoader.getResourceAsStream("etc/regions.xml").

This is a blocker for applications that must work offline, but rely on code calling the AWS SDK.