Add support for Summon environments

[izgeri]

Summon supports an environment flag which allows you to specify different variables for different app environments (eg dev, prod, etc)

The secrets.yml syntax in that case would look something like this:

common:
  ACCOUNT: my-account
  SHARED_PASSWORD: SuperSecret

dev:
  CLUSTER_NAME: !var dev/cluster-name
  ZONE: !var dev/zone

prod:
  CLUSTER_NAME: !var prod/cluster-name
  ZONE: !var prod/zone

where the variables in common are loaded regardless of environment and the variables in dev / prod are only loaded when the environment specified is dev or prod (respectively).

The buildpack should support an environment variable (perhaps SUMMON_ENV_KEY_NAME as here?) that allows the user to specify the value of environment the buildpack should use to load the correct variables for the app env.

[izgeri]

Note that the conjur-env binary that is built into the buildpack uses the Summon secretsyml library to parse the Summon configuration from file here, and in the Summon binary the same secretsyml command is used to parse a file except it passes in the value of the environment configuration parameter here

This fix should involve updating the conjur-env binary to check for the SUMMON_ENV_KEY_NAME environment variable and to pass it to the ParseFromFile command, if it exists.

[sgnn7]

@izgeri I would amend your comment a bit:

• SUMMON_ENV_KEY_NAME is what ends up in the child process env as a variable that holds the env that you set
• -e/--environment is the actual flag that you pass to summon to set it

If we have to set a variable to pass into a binary of ours, it would make sense that we call it just <name>_ENV (e.g. SUMMON_ENV or CONJUR_ENV) or just ENVIRONMENT.