feat(snap): use updated environment variable injection

[MonicaisHer]

For details on the new scheme for setting environment variables, please refer to edgexfoundry/edgex-go#3986.
Signed-off-by: Mengyi Wang [email protected]

If your build fails due to your commit message not passing the build checks, please review the guidelines here: https://github.com/edgexfoundry/device-rest-go/blob/main/.github/Contributing.md

PR Checklist

Please check if your PR fulfills the following requirements:

• I am not introducing a breaking change (if you are, flag in conventional commit message with BREAKING CHANGE: describing the break)
• I am not introducing a new dependency (add notes below if you are)
• I have added unit tests for the new feature or bug fix (if not, why?) N/A - they are in the imported module Add tests for snap config options canonical/edgex-snap-testing#53
• I have fully tested (add details below) this the new feature or bug fix (if not, why?)
• I have opened a PR for the related docs change (if not, why?)

Testing Instructions

1. set up:

snap install edgexfoundry --edge
snap install edgex-device-rest --channel="edge/pr-177"

2. Enable config and set a global config value:

$ snap set edgex-device-rest config-enabled=true
$ snap set edgex-device-rest config.service-startupmsg="testing injection"

$ snap start edgex-device-rest
Started.

$ snap logs -n=all edgex-device-rest | grep "testing injection"
...

3. Set a app-specific value:

$ snap set edgex-device-rest apps.device-rest.config.service-port=11111

$ snap restart edgex-device-rest
Restarted.

$ snap logs -n=all edgex-device-rest | grep "11111"
msg="Web server starting (localhost:11111)"

New Dependency Instructions (If applicable)

[farshidtz]

Looks good. Thanks.

$ snap install edgex-device-rest --channel="edge/pr-177"
edgex-device-rest (edge/pr-177) 2.0.1-dev.14 from Canonical✓ installed

$ snap set edgex-device-rest config.service-startupmsg="testing injection"
error: cannot perform the following tasks:
- Run configure hook of "edgex-device-rest" snap (run hook "configure": 
-----
edgex-device-rest.configure: could not process options: 'config.' and 'apps.' options are allowed only when config-enabled is true.

WARNING: Setting config-enabled=true will unset existing 'env.' options and ignore future sets!!
-----)
# the above error was expected

$ snap set edgex-device-rest config-enabled=true
$ snap set edgex-device-rest config.service-startupmsg="testing injection"
$ snap start edgex-device-rest
Started.
$  snap logs -n=all edgex-device-rest | grep "testing injection"
2022-04-26T10:51:16+02:00 edgex-device-rest.device-rest[46017]: level=INFO ts=2022-04-26T08:51:16.959910144Z app=device-rest source=variables.go:352 msg="Variables override of 'Service.StartupMsg' by environment variable: SERVICE_STARTUPMSG=testing injection"
2022-04-26T10:51:17+02:00 edgex-device-rest.device-rest[46017]: level=INFO ts=2022-04-26T08:51:17.25412312Z app=device-rest source=message.go:55 msg="testing injection"


$ snap set edgex-device-rest apps.device-rest.config.service-port=11111
$ snap restart edgex-device-rest
Restarted.
$ snap logs -n=all edgex-device-rest | grep "11111"
2022-04-26T10:51:36+02:00 edgex-device-rest.device-rest[46210]: level=INFO ts=2022-04-26T08:51:36.016478222Z app=device-rest source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T10:51:36+02:00 edgex-device-rest.device-rest[46210]: level=INFO ts=2022-04-26T08:51:36.028125377Z app=device-rest source=variables.go:352 msg="Variables override of 'Service.Port' by environment variable: SERVICE_PORT=11111"
2022-04-26T10:51:36+02:00 edgex-device-rest.device-rest[46210]: level=INFO ts=2022-04-26T08:51:36.054827968Z app=device-rest source=httpserver.go:123 msg="Web server starting (localhost:11111)"