Docker-compose disable healthcheck properly handled

Previously, if a container had healthchecks disabled in the
docker-compose.yml file and the user did a `podman inspect <container>`,
they would have an incorrect output:

```
"Healthcheck":{
   "Test":[
      "CMD-SHELL",
      "NONE"
   ],
   "Interval":30000000000,
   "Timeout":30000000000,
   "Retries":3
}
```

After a quick change, the correct output is now the result:
```
"Healthcheck":{
   "Test":[
      "NONE"
   ]
}
```

Additionally, I extracted the hard-coded strings that were used for
comparisons into constants in `libpod/define` to prevent a similar issue
from recurring.

Closes: #14493

Signed-off-by: Jake Correnti <jcorrenti13@gmail.com>

test/compose/disable_healthcheck/docker-compose.yml

@@ -0,0 +1,10 @@
+version: "3.7"
+services:
+  noHc:
+    image: alpine
+    container_name: noHc
+    ports:
+      - "4000:80"
+    restart: unless-stopped
+    healthcheck:
+      disable: true

test/compose/disable_healthcheck/tests.sh

@@ -0,0 +1,2 @@
+podman inspect --format='{{.Config.Healthcheck.Test}}' noHc
+like $output "[NONE]" "$testname: healthcheck properly disabled"