Add DeploymentContext.modify_yaml helper

For custom deploy commands

stack_orchestrator/data/stacks/fixturenet-optimism/deploy/commands.py

@@ -14,7 +14,6 @@
 # along with this program.  If not, see <http:#www.gnu.org/licenses/>.
 
 from stack_orchestrator.deploy.deployment_context import DeploymentContext
-from ruamel.yaml import YAML
 
 
 def create(context: DeploymentContext, extra_args):
@@ -23,17 +22,12 @@ def create(context: DeploymentContext, extra_args):
     # deterministic-deployment-proxy contract, which itself is a prereq for Optimism contract deployment
     fixturenet_eth_compose_file = context.deployment_dir.joinpath('compose', 'docker-compose-fixturenet-eth.yml')
 
-    with open(fixturenet_eth_compose_file, 'r') as yaml_file:
-        yaml = YAML()
-        yaml_data = yaml.load(yaml_file)
-
     new_script = '../config/fixturenet-optimism/run-geth.sh:/opt/testnet/run.sh'
 
-    if new_script not in yaml_data['services']['fixturenet-eth-geth-1']['volumes']:
-        yaml_data['services']['fixturenet-eth-geth-1']['volumes'].append(new_script)
+    def add_geth_volume(yaml_data):
+        if new_script not in yaml_data['services']['fixturenet-eth-geth-1']['volumes']:
+            yaml_data['services']['fixturenet-eth-geth-1']['volumes'].append(new_script)
 
-    with open(fixturenet_eth_compose_file, 'w') as yaml_file:
-        yaml = YAML()
-        yaml.dump(yaml_data, yaml_file)
+    context.modify_yaml(fixturenet_eth_compose_file, add_geth_volume)
 
     return None