Create a Lease Manager that's capable of getting a secret

[fmitchell-r7]

The starting point for the LeaseManager class should be that it's capable of getting a secret. See #4 for the class interface. Tests around the Lease Manager should include:

• The default status is PENDING
• The status changes to READY when SecretProvider#initialize() succeeds
• The status changes to PENDING when SecretProvider#initialize() fails
• The default data is null
• The data changes to a secret when SecretProvider#initialize() succeeds
• The data changes to null when SecretProvider#initialize() fails
• A "ready" event is emitted when SecretProvider#initialize() succeeds
• SecretProvider#initialize() is called repeatedly until it succeeds