Prevent restart loop

This code would prevent Xinit from restarting a wiki several times in a row. What usually happens is that when XWiki freezes for some reasons, it might be restarted by a upcoming check_proc, or if check_http has too low  settings to permit XWiki to respond fast enough. So idea is to make use of Maintenance mode to avoid these unwanted restarts. 
Subshell is used to put the sleep command in background. If something interrupts this subshell (eg. user disconnects, xwiki.sh gets killed), the maintenance file will be removed.