Senza patch might destroy user data by accident

[hjacobs]

$ senza patch --user-data 'foo: bar' slo-metrics
Patching Auto Scaling Group slo-metrics-9-AppServer-U3AL15Y4689O..
{'IamInstanceProfile': 'slo-metrics-9-AppServerInstanceProfile-INEECMIQC7AH', 'UserData': "#taupage-ami-config\napplication_id: zmon-slo-metrics\napplication_version: '9'\nenvironment:\n  DATABASE_URI: host=zmon-slo-metrics.xxx.amazonaws.com\n    user=zsm dbname=zmon_slo_metrics password=xxx\n  KAIROSDB_URL: https://data-service.example.org/kairosdb-proxy\n  OAUTH2_ACCESS_TOKEN_URL: https://token.example.org/oauth2/access_token?realm=/services\nfoo: bar\nhealth_check_path: /health\nmint_bucket: zalando-stups-mint-123-eu-central-1\nnotify_cfn:\n  resource: AppServer\n  stack: slo-metrics-9\nports:\n  8080: 8080\nruntime: Docker\nsource: registry.opensource.zalan.do/zmon/zmon-slo-metrics:9\n", 'AssociatePublicIpAddress': False, 'ImageId': 'ami-5fd72b30', 'InstanceMonitoring': {'Enabled': True}, 'SecurityGroups': ['sg-a7305fcf'], 'BlockDeviceMappings': [], 'InstanceType': 't2.micro', 'LaunchConfigurationName': 'slo-metrics-9-AppServerConfig-KQ83GUQQHTO2-20161104T120253', 'ClassicLinkVPCSecurityGroups': [], 'EbsOptimized': False}

Missing a single character (the space after the colon) will make the given YAML load as a single string and results in "destroying" the Taupage userdata:

$ senza patch --user-data 'foo:bar' slo-metrics
Patching Auto Scaling Group slo-metrics-9-AppServer-U3AL15Y4689O..
{'UserData': 'foo:bar', 'IamInstanceProfile': 'slo-metrics-9-AppServerInstanceProfile-INEECMIQC7AH', 'InstanceMonitoring': {'Enabled': True}, 'AssociatePublicIpAddress': False, 'SecurityGroups': ['sg-a7305fcf'], 'LaunchConfigurationName': 'slo-metrics-9-AppServerConfig-KQ83GUQQHTO2-20161104T120307', 'BlockDeviceMappings': [], 'EbsOptimized': False, 'InstanceType': 't2.micro', 'ImageId': 'ami-5fd72b30', 'ClassicLinkVPCSecurityGroups': []}