If a user specifies a header in their request for metadata,
it could override what the proxy would have inserted on their
behalf. Make sure to remove any headers we don't want, and
override something that might be present in the request.
If the agent somehow gets a request with both headers it will
silently drop it.
Change-Id: Id6c103b7bcebe441c27c6049d349d84ba7fd15a6
Closes-bug: #1865036
(cherry picked from commit 5af046fd4e)
1c13ad05dd