userportal,webadmin: BrandingManager fails with missing etcdir

- BrandingManager.getInstance() would fail when you have a missing
etcDir configuration which is often the case in unit tests. This
patch stops the failure and instead returns no branding information.

Change-Id: Ifc34286323c1eda114f6a8b5570274faf53b566c
Signed-off-by: Alexander Wels <awels@redhat.com>