webadmin: Fix FB issues in AsyncDataProvider

Fix FindBugs issues (members that should have been static) introduced by
commit 69e57dc94cc30652caa7b790bd5e9a94816b6d8d.

Change-Id: I1dd37f91f0b53b3e334d17082839876529ee9bc5
Signed-off-by: Allon Mureinik <amureini@redhat.com>