Mangler that sets UnavailableOnStartupException on all WebAppContexts to true (or to defined value). It does so by
"crawling" all the defined contexts in Jetty instance. Note: use of this handler is limited only before Jetty is
started (for obvious reasons)! It returns the count of affected WebAppContext encountered during it's work being done
(in other words, returns the count of the setter invocations it did).
for ( int i = 0; i < handlers.length; i++ )