Add support for additional parameters on custom bootstrap (#2927)

Previous to this commit, if a user would ever like to add parameters to the custom bootstrap script call, they would need to configure Patroni like this:

```
bootstrap:
  method: custom_method_name
  custom_method_name:
    command: /path/to/my/custom_script --arg1=value1 --arg2=value2 ...
```

This commit extends that so we achieve a similar behavior that is seen when using `create_replica_methods`, i.e., we also allow the following syntax:

```
bootstrap:
  method: custom_method_name
  custom_method_name:
    command: /path/to/my/custom_script
    arg1: value1
    arg2: value2
```

All keys in the mapping which are not recognized by Patroni, will be dealt with as if they were additional named arguments to be passed down to the `command` call.

References: PAT-218.

features/backup_restore.py

@@ -6,6 +6,7 @@ if __name__ == "__main__":
     parser = argparse.ArgumentParser()
     parser.add_argument("--datadir", required=True)
     parser.add_argument("--sourcedir", required=True)
+    parser.add_argument("--test-argument", required=True)
     args, _ = parser.parse_known_args()
 
     shutil.copytree(args.sourcedir, args.datadir)

features/environment.py

@@ -892,22 +892,28 @@ class PatroniPoolController(object):
         }
         self.start(to_name, custom_config=custom_config)
 
+    def backup_restore_config(self, params=None):
+        return {
+            'command': (self.BACKUP_RESTORE_SCRIPT
+                        + ' --sourcedir=' + os.path.join(self.patroni_path, 'data', 'basebackup')).replace('\\', '/'),
+            'test-argument': 'test-value',  # test config mapping approach on custom bootstrap/replica creation
+            **(params or {}),
+        }
+
     def bootstrap_from_backup(self, name, cluster_name):
         custom_config = {
             'scope': cluster_name,
             'bootstrap': {
                 'method': 'backup_restore',
-                'backup_restore': {
-                    'command': (self.BACKUP_RESTORE_SCRIPT + ' --sourcedir='
-                                + os.path.join(self.patroni_path, 'data', 'basebackup').replace('\\', '/')),
+                'backup_restore': self.backup_restore_config({
                     'recovery_conf': {
                         'recovery_target_action': 'promote',
                         'recovery_target_timeline': 'latest',
                         'restore_command': (self.ARCHIVE_RESTORE_SCRIPT + ' --mode restore '
                                             + '--dirname {} --filename %f --pathname %p').format(
                             os.path.join(self.patroni_path, 'data', 'wal_archive_clone').replace('\\', '/'))
-                    }
-                }
+                    },
+                })
             },
             'postgresql': {
                 'authentication': {
@@ -928,11 +934,7 @@ class PatroniPoolController(object):
                     .format(os.path.join(self.patroni_path, 'data', 'wal_archive').replace('\\', '/'))
                 },
                 'create_replica_methods': ['no_leader_bootstrap'],
-                'no_leader_bootstrap': {
-                    'command': (self.BACKUP_RESTORE_SCRIPT + ' --sourcedir='
-                                + os.path.join(self.patroni_path, 'data', 'basebackup').replace('\\', '/')),
-                    'no_leader': '1'
-                }
+                'no_leader_bootstrap': self.backup_restore_config({'no_leader': '1'})
             }
         }
         self.start(name, custom_config=custom_config)

features/steps/standby_cluster.py

@@ -15,9 +15,7 @@ def start_patroni(context, name, cluster_name):
         "scope": cluster_name,
         "postgresql": {
             "callbacks": callbacks(context, name),
-            "backup_restore": {
-                "command": (context.pctl.PYTHON + " features/backup_restore.py --sourcedir="
-                            + os.path.join(context.pctl.patroni_path, 'data', 'basebackup').replace('\\', '/'))}
+            "backup_restore": context.pctl.backup_restore_config()
         }
     })