aaa: filters: enable accept engine session using header

new header OVIRT-INTERNAL-ENGINE-AUTH-TOKEN accepts token that contains
engine session id.

a new query GetEngineSessionIdToken returns this token.

ui should use the new query and apply the header to avoid double login.

this may be temporary solution for 3.5 life cycle, as such applied only
for restapi.

when engine session is invalidated, all instances that used it are also
invalidated.

Change-Id: I028082cced7043b5af0b9fa7b0548ba888996e9d
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1161734
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1161730
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>