Implement "OnFailure" option to create stack

We need to support the different options here.

This is normally the first or second question asked about heat.

Asked many times at summit and on IRC.

We seem to be implementing DO_NOTHING only.

See:
http://docs.amazonwebservices.com/AWSCloudFormation/latest/APIReference/API_CreateStack.html
OnFailure: DO_NOTHING, ROLLBACK, or DELETE

shardy:

Related - we need to implement rollback before we can implement the ROLLBACK option, ref #154 - I've looked into this but not got around to implementing yet - should basically just be a special type of update (to the previous template).

I've also had several questions around rollback and "atomic stack launch" functionality recently, so will try to look into this in the next few weeks. Since #154 is already assigned to me, I'll take this issue (unless anyone else wants to do it :)