retries, ping timeout, sql mock handler

[scottlepp]

• support retries - for situations where the db is temporarily unavailable
• use timeout setting when pinging - there is a timeout setting but ping didn't use it
• sql mock driver registry
  • allow providing a handler to handle ping, results - provides more control when mocking a driver

[yesoreyeram]

LGTM. any reason csv_mock.go was moved outside? Keeping the mock outside on its own package is suggested.

[scottlepp]

@yesoreyeram yes there is a circular dependency :(

EDIT: fixed