*: switch to github.com/ghodss/yaml for more consistent YAML parsing

ghodss/yaml converts from YAML to JSON before attempting to unmarshal.
This allows us to:

* Get the correct behavor when decoding base64'd []byte slices.
* Use *json.RawMessage.
* Not have to support extravagant YAML features.
* Let our structs use `json:` tags

connector/mock/connectortest.go

@@ -69,8 +69,8 @@ func (c *CallbackConfig) Open() (connector.Connector, error) {
 // PasswordConfig holds the configuration for a mock connector which prompts for the supplied
 // username and password.
 type PasswordConfig struct {
-	Username string `yaml:"username"`
-	Password string `yaml:"password"`
+	Username string `json:"username"`
+	Password string `json:"password"`
 }
 
 // Open returns an authentication strategy which prompts for a predefined username and password.