Support Parsoid on private wikis

Parsoid has no special access to anything.  Since officewiki is private parsoid
cant read it.  We need to pass along the user's cookies that granted access to
the wiki so that parsoid may use them as necessary.

This is temporary support.  Gabriel suggested that in the future we migrate to the
PHP Virtual REST Service and through that share code between Flow, VE and anything
else that wants to talk with parsoid.

Change-Id: Ib5e997d09d6e8a3b8f0205feabe301e7eb2fb537
Merge "Support Parsoid on private wikis"