OPENDJ-2027 Code cleanup

Preparatory work for OPENDJ-2027:
* src/main/java/org/opends/server/backends/jeb/DBTest.java
** Reduce visibilty of printMessage and rename it to printErrorMessage to improve code consistency
* src/main/java/org/opends/server/tools/ConfigureWindowsService.java
* src/main/java/org/opends/server/tools/StartWindowsService.java
* src/main/java/org/opends/server/tools/StopWindowsService.java
** Autorefactor'ed file + format
** Use straigt return
** Remove unecessary comment
** Additionnal minor cleanup
** Extract method serviceState() to avoid multiple nullchecks on output streams.
* Changes in other files are related to the serviceState() extracted method