Cleanup comment cruft and spec ordering

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Move logging statement to reduce duplicate conditional

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Remove redundant log message

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Add Container#link method

  * only Container has knowledge about warden protocol

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>
Instance#promise_link uses Container

Signed-off-by: Maria Shaldibina <mariash@pivotallabs.com>