Tolerate lookup failures in Fn::Select

A wait condition will return an empty dict for its Data attribute
until it has been created, however Fn::Select on Data will be evaluated
before the wait condition is created (for example, during stack-list
or stack-show). The current error raising of Fn::Select leads these
operations to fail.

This change results in Fn::Select evaluation behaving in the
following way:
- KeyError on dict lookup failure results in empty string
- IndexError on list index results in empty string
- Passing an empty string as the value results in an empty string

Closes-Bug: #1243958
Change-Id: I3b01c8ce5dc56e804016274282d2ee69f539bf40
Delete deprecated docs/ directory

I think we have deprecated this directory long enough.
We have proper getting started guides and api docs on openstack.org

Change-Id: Iaee690046866b98eea9a206dc6f2dca9b9af18b6
use exception str() not .message

This mostly fixes the accesses to .message, there is still the
translation that is using the .message.

Partial-bug: #1243883
Change-Id: I709f65e39c017d70eaca5d8f6d06e0227b67e816
Merge "Tolerate lookup failures in Fn::Select"
Merge "Delete deprecated docs/ directory"