Fix creating complement_of! query for single manager_uuid

[slemrmartin]

With one manager_uuid it created query like this:

SELECT * FROM (VALUES ('node-uuid'),) AS active_entities_table('source_ref') (unwanted comma after VALUES)

cc @agrare @Ladas

[slemrmartin]

@Ladas it means this is not covered by specs, please add it to place where you are testing this

[Ladas]

@slemrmartin could you add the spec please? E.g. to retention_strategies_spec. We should probably test for multiple variants of manager ref (e.g. of sizes 0, 1 and 2)

[miq-bot]

Checked commits https://github.com/slemrmartin/inventory_refresh/compare/6002368ba9c63de88b67b3bcb463d6708d6dd6c4~...1a47bfdab281cad08e47390c814bef6ce77b0194 with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0 2 files checked, 1 offense detected

spec/persister/retention_strategies_spec.rb

• [ ] :warning: - Line 34, Col 11 - Lint/UselessAssignment - Useless assignment to variable - vm2.