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).
Tricky to cleanly always do the check before acting, without duplicating the checks (even if the code is reused by extracting to a shared method). I'm inclined to rely on `builder.globalPropertiesFile` not breaking if you give it a file that does not exist. It won't give a particularly nice warning (it might even ignore silently!). If the file is deleted between our first check and the builder doing its stuff then so be it.

Removing duplicate checks from `checkFilePermissionsX00`