burnin: Filter flavors based on 'SNF:allow_create'

Filter out flavors that are not allowed to create a machine.
Update snf-ci to support the same functionality.
snf-ci: Fix a typo in SynnefoCI '__init__'

Replace 'kamaki_cloud' variable with 'self.kamaki_cloud' property.
astakos: Show label adjacent to checkbox

Closes #38
pithos: Reject XML in uploads with hashmap

Do not accept XML formatted request body