feat(extensions): add user skipped task hook

refs TryGhost#308, TryGhost#1115

Author: vikaspotluri123

extensions/systemd/index.js

@@ -22,6 +22,10 @@ class SystemdExtension extends Extension {
                 }
 
                 return false;
+            },
+            onUserSkip: ({instance, ui}) => {
+                ui.log('Systemd setup skipped, reverting to local process manager', 'yellow');
+                instance.config.set('process', 'local').save();
             }
         }];
     }

extensions/systemd/test/extension-spec.js

@@ -24,7 +24,7 @@ describe('Unit: Systemd > Extension', function () {
         expect(tasks[0].id).to.equal('systemd');
         expect(tasks[0].name).to.equal('Systemd');
 
-        const [{enabled, task, skip}] = tasks;
+        const [{enabled, task, skip, onUserSkip}] = tasks;
         const config = configStub();
         const instance = {config, name: 'test_instance'};
 
@@ -55,6 +55,11 @@ describe('Unit: Systemd > Extension', function () {
 
         expect(skip({instance})).to.be.false;
         expect(exists.calledOnce).to.be.true;
+
+        config.set.resetHistory();
+        expect(onUserSkip).to.be.a('function');
+        onUserSkip({instance});
+        expect(config.set.calledOnceWithExactly('process', 'local')).to.be.true;
     });
 
     describe('setup stage', function () {

lib/commands/setup.js

@@ -141,6 +141,10 @@ class SetupCommand extends Command {
 
                 const confirmed = await this.ui.confirm(`Do you wish to set up ${name}?`, true);
                 if (!confirmed) {
+                    if (step.onUserSkip) {
+                        await step.onUserSkip(ctx);
+                    }
+
                     return task.skip();
                 }