Add config for boto https_validate_certificates

Boto does not, by default, validate https ceritificates on endpoints. We
now provide a way to specify it in the heat configuration along side
is_secure. Heat deployers may also need to turn this off if boto ever
does make it default and they want to use self signed certs.

Fixes bug #1130345

Change-Id: I09b684dd28a8a57c6ce514d1df1e699e7c8b182e
Merge "Add config for boto https_validate_certificates"