brooklyn.properties permissions check

This change will cause brooklyn to fail to start if brooklyn.properties do not have permission x00 (e.g. 400, 600 or 700).

e.g.:

    brooklyn launch --localBrooklynProperties localBrooklyn.properties 
     _                     _    _             
    | |__  _ __ ___   ___ | | _| |_   _ _ __ (R)
    | '_ \| '__/ _ \ / _ \| |/ / | | | | '_ \ 
    | |_) | | | (_) | (_) |   <| | |_| | | | |
    |_.__/|_|  \___/ \___/|_|\_\_|\__, |_| |_|
                                  |___/             0.7.0-SNAPSHOT
    
    2014-08-08 18:31:48,829 ERROR Startup error: Invalid permissions for file localBrooklyn.properties; expected 600 but was -rw-r--r--
    Startup error: Invalid permissions for file localBrooklyn.properties; expected 600 but was -rw-r--r--

Note the "Adds FileUtil" commit is a duplicate of code in PR #114. Suggest we merge that one first (depending which one folk get around to reviewing first).
`checkFileReadable()` test also performed by calling method, so arguable not required (although I think this should be a generic utility method).

"Check-then-act" is a race condition; suggest handling both cases identically (ideally without duplicating code).