Allow default value for log

Get a non-null default value for log level of it is not available on environment
variables.

server/org.jboss.tools.vscode.java/src/org/jboss/tools/vscode/java/handlers/LogHandler.java

@@ -34,7 +34,7 @@ public class LogHandler {
 
 	public void install(JavaClientConnection rcpConnection) {
 	    this.dateFormat = DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
-	    this.logLevelMask = getLogLevelMask(System.getProperty("log.level"));
+	    this.logLevelMask = getLogLevelMask(System.getProperty("log.level", ""));//Empty by default
 	    this.calendar = Calendar.getInstance();
 	    this.connection = rcpConnection;