When using BB_FETCH_PREMIRRORONLY we write to the datastore to disable the network.
This change needs to be undo when handling later urls, so operate on a copy of the
datastore to allow this.
Reported by Julian Haller <julian.haller@philips.com>
(Bitbake rev: 67a5ede8ae92ed7dcad29fd0dcfd62c6640b10b2)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>