webadmin: Fix coverity defect CID 1230277

Not sure why the executeCommand() overload with parameters was
overridden here as no command in the dialog accepts
parameters. Simplified the code a bit, which should also please
Coverity.

Change-Id: Ie9fb33a37dd76a27fbc6948018d1ec2a6f495239
Signed-off-by: Lior Vernia <lvernia@redhat.com>