[sonic-package-manager] stop service explicitelly before uninstalling…

… package (sonic-net#1805)

#### What I did

Fixed an issue with uninstall.
1. When disabling the feature by setting its state to disabled in FEATURE table and then uninstalling it, there is a possibility that service hasn't fully stopped yet.
2. When uninstalling with --force option, and reinstalling the package with --enable option the service does not start.

#### How I did it
Stop and disable service explicitely before uninstalling package.

#### How to verify it

```
sudo spm uninstall cpu-report --force && sudo spm install cpu-report=10.0.0 -v DEBUG -y --enable && docker ps
```

sonic_package_manager/manager.py

@@ -435,6 +435,17 @@ def uninstall(self, name: str, force=False):
         # After all checks are passed we proceed to actual uninstallation
 
         try:
+            # Stop and disable the service.
+            # First to make sure we are not uninstalling
+            # package before the service has fully stopped
+            # since "config feature state" command is not blocking.
+            # Second, we make sure the service is in disabled state
+            # so that after reinstall and enablement hostcfgd will enable
+            # it and start it.
+            # TODO: once there is a way to block till hostcfgd will stop
+            # the service, replace it with new approach.
+            self._systemctl_action(package, 'stop')
+            self._systemctl_action(package, 'disable')
             self._uninstall_cli_plugins(package)
             self.service_creator.remove(package)
             self.service_creator.generate_shutdown_sequence_files(