Fix for InCallUI finishing too quickly to display error dialog

Increase the delay before disconnecting the call for
DisconnectCause.ERROR, so that the user has time to acknowledge
the error.

To avoid regressing on b/20956721, keep track of any calls
that are pending a disconnect. If the user has explicitly dismissed
the error dialog, disconnect the call immediately to avoid blocking
the UI any further.

Bug: 21436856
Change-Id: I339cdbf1ba99fda5b1f5c8c31f722c97b64f487f