RFR 9: 8167192 [Testbug] : java/io/Serializable/serialFilter test conditions wrong

[Roger Riggs]

Please review a test correction to the permissions granted to the test
and the check that the global filter cannot be re-set if once set.
Removed unnecessary code supplying a OIS when testing setting the global 
filter.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-filtertest-8167192/

Thanks, Roger