GitLab

Include flag with each download to indicate if its allowed to proceed
over metered networks.  Downloads are left in WAITING_FOR_NETWORK
state, similar to how ALLOWED_NETWORK_TYPES is handled.

Also keep blocked downloads in WAITING_FOR_NETWORK state instead
of marking them as failed.

Bug: 3001465, 5734560
Change-Id: I80bb9aa9bd25ddf6f7a2472db344b6ba6878bd74