restapi: set Application mode in current when session is reused

   When client calls REST API with 'prefer: persistent-auth'
header and valid session ID, LoginValidator.validate(String sessionId)
will be called. But in this case application mode is not being
set in Current. Because of this, rsdl is returned with all the
links includeing data center and vm though the engine is running
only in GlusterOnly mode.

Change-Id: I972d62e2bad77b6674bf8666ed4aa041bf8319e0
Bug-Url: https://bugzilla.redhat.com/1042740
Signed-off-by: Ramesh Nachimuthu <rnachimu@redhat.com>