tests: Fixed start and stop methods in xstartserv. Now waitpid() is only used...

tests: Fixed start and stop methods in xstartserv. Now waitpid() is only used to cleanup any zombie processes while /proc/<pid> is checked if the process does run.

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@2505 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534