Fixes #3380

Adds address_mode to checks (but no auto) and allows services and checks
to set literal port numbers when using address_mode=driver.

This allows SDNs, overlays, etc to advertise internal and host addresses
as well as do checks against either.

Rely less on the mockConsulServiceClient because the real
consul.ServiceClient needs all the testing it can get!

Previously if only an interpolated variable used in a service or check
was changed we interpolated the old and new services and checks with the
new variable, so nothing appeared to have changed.

Also skip getting an address for script checks which don't use them.

Fixed a weird invalid reserved port in a TaskRunner test helper as well
as a problem with our mock Alloc/Job. Hopefully the latter doesn't cause
other tests to fail, but we were referencing an invalid PortLabel and
just not catching it before.

Fixes #3620

Previously we concatenated tags into task service IDs. This could break
deregistration of tag names that contained double //s like some Fabio
tags.

This change breaks service ID backward compatibility so on upgrade all
users services and checks will be removed and re-added with new IDs.

This change has the side effect of including all service fields in the
ID's hash, so we no longer have to track PortLabel and AddressMode
changes independently.