Return the original upstream response body when the the list request
returns an error. In general, the provider is returning useful and
actionable error messages for the user, the previous code hid this in
the logs and this is easy for user to overlook.

Additionally, remove an early return from error case after fetching
metrics. This looked like a bug and could result in empty api responses
if there was a prometheus error.

Signed-off-by: Lucas Roesler <roesler.lucas@gmail.com>

* Add service target metric
* Add service min replicas metric
* Add scale type metric

These combined allow new auto-scaling modes and parameters
for OpenFaaS Pro customers.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

Signed-off-by: Vivek Singh <vivekkmr45@yahoo.in>

The function deployment and status structs have been moved away
into the faas-provider package.

Tested with a build, running tests, and CI.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

The unit tests were inside the `gateway/tests` directory which had no
effect to the coverage for `go test`. Therefore, moved the tests inside
the same directory as the test target.

Signed-off-by: Ken Fukuyama <kenfdev@gmail.com>

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

Signed-off-by: Alex Ellis <alexellis2@gmail.com>