restapi : NullPointerException when Authorization header is passed(#916085)

When invalid authorization header is passed a null pointer
exception is thrown on the server resulting in internal
server error.

Change-Id: I10b580dcc3fddbec8ccd80130e977aeb4ef37fb2
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=916085
Signed-off-by: Ravi Nori <rnori@redhat.com>