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).
`FileUtil` (and thus these methods) was added in PR #114 

Problem is its implementation is based on `File.setReadable(boolean readable, boolean ownerOnly)`, so it would need to interpret the hex and make appropriate set of calls. And then we'd throw away the code when we can use Java 7. Let's refactor when we have more than a requirement for `setFilePermissionsTo600` and `setFilePermissionsTo700` - they are both marked `@Beta`.