engine: supress findbugs warnings in GlusterUtil

When compiling the autoclosable syntax in Java 7, certain compilers
may create bytecode that contains redundant null checks in it.

Change-Id: I3d60d51747be3908fb78427b50698c6d4d8d9ac0
Signed-off-by: Alissa Bonas <abonas@redhat.com>