webadmin: Bypassing findbugs issue of incorrect lazy initialization.

Findbug is referencing a potential threading issue where in a multi
thread environment, there would be potential situation where the lazy
initialization of windowsOsTypes in AsyncDataProvider:getWindowsOsTypes()
will creat more than once instnace.

With GWT, synchronizing the method has no meaning except
bypassing findbugs warning as the code compiles to
javascript and is executed in single thread anyway.

Change-Id: I599d8418bf6e326564354e6173603fd974af1a7a
Signed-off-by: Asaf Shakarchi <asaf@redhat.com>