Fetch Jenkins data with credentials included

If Jenkins requires authentication and it is hosted on a different
origin than Gerrit (which probably is the case) then the request will
fail with 403.

With "credentials = include" cookies are sent. So if I am logged in
Jenkins, the request will succeed and no explicit credentials passing is
required.

Change-Id: I3a9ce7911fd8c6472c99828dad347e68aced4ce6