adds katello.tests.distributors namespace. Also adds distributor
test: If an organization has no environments, the "+New Distributor"
button is disabled.
distributor test now checks for the correct warn message
renamed predicate to make its purpose clearer
removed unused imports from distributors.clj
Merge pull request #561 from blrm/distributor-test

UI: "+ New Distributor" is not available until atleast one environment is present