Update Vault setup

[anncatton]

Just a placeholder ticket, dac-api has a direct connection to vault in its startup script so may need to consider updating this to match new devops approach

Update 24/09/16: We are moving away from the old vault approach for all services, so this will need to be implemented as soon as the new cluster setup is available.

TODO:

• move all secret values to AppConfig. These values will be available in the container on deployment
• remove previous Vault access setup in vault.ts, secrets.ts
• update secret values references as necessary where they are accessed in the codebase
• may be a good PR to remove old ega email implementation as well (which includes secret values)
• will need to keep an async portion of server startup to accommodate the public key access included for ega reconciliation.