Resolve "Database initialization if empty db detected."

Closes #3025 (closed).

• a7df1a2c automatic init of mysql schema

• 0ea80485 convert db access params to kea-admin

• 7291a857 automatic init of postgresql schema

• 60ed62a2 add ability to inherit env in ProcessSpawn

• 6fdfb492 minor changes to kea-admin

  • Reword 'Database version' to 'Schema version'.
  • Remove a newline that was present only when running mysql operations and not for postgresql operations. It was more visible since now it appeared in the kea logs.
  • Remove some extraneous exits. They weren't in the way of anything, but weren't doing anything either.

• db869d13 switch io service to DatabaseConnection's

• 34bad492 add db init on startup to other managers

• edd0cbe6 add ability to wait sync in ProcessSpawn

• ad113f14 sync kea-admin in db connection and fix interaction with retry

• 7229b901 add unit tests

• ea8fd214 document automatic db init

• bbb97c46 add ChangeLog entry