This commits changes the behaviour in a case there was an error while
interacting with EC2 tags related to the CloudFormation Distribution
resource, fixing the issue with nil pointer dereference when despite
an error being present code path to handle tags was executed.
Also, a small re-factor of the `validateHTTP` helper method,
and a unit test added for it.
Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>