Fixes #21808 - Correct DockerTag unit import

[parthaa]

Before This commit

::Katello::DockerTag.import_for_repository(repo)
would not update an existing repo. It would not clear the prior
tags before importing new ones from pulp.
This call in particular is used by the promotion operations to update
tags in a CVE repository.

After This commit

This operation is now fixed because the import for repository forcibly
clears out existing tags in the repo before the import actually starts.

[theforeman-bot]

Issues: #21808

[akofink]

Probably because I waited so long on testing this PR, but I'm getting this error on Actions::Katello::ContentView::Publish:

NoMethodError: undefined method `ignore_global_proxy' for #<Katello::Repository:0x0000000f805e58>
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/activemodel-4.2.9/lib/active_model/attribute_methods.rb:433:in `method_missing'
/home/vagrant/katello/app/models/katello/glue/pulp/repo.rb:218:in `proxy_host_value'
/home/vagrant/katello/app/models/katello/glue/pulp/repo.rb:249:in `importer_connection_options'
/home/vagrant/katello/app/lib/actions/katello/repository/create.rb:15:in `block in plan'
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/dynflow-0.8.33/lib/dynflow/execution_plan.rb:346:in `call'
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/dynflow-0.8.33/lib/dynflow/execution_plan.rb:346:in `switch_flow'
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/dynflow-0.8.33/lib/dynflow/action.rb:381:in `sequence'
/home/vagrant/katello/app/lib/actions/katello/repository/create.rb:14:in `plan'
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/dynflow-0.8.33/lib/dynflow/action.rb:473:in `block (3 levels) in execute_plan'
/home/vagrant/.rvm/gems/ruby-2.2.4/gems/dynflow-0.8.33/lib/dynflow/middleware/stack.rb:26:in `call'
...

[parthaa]

Probably because I waited so long on testing this PR, but I'm getting this error on Actions::Katello::ContentView::Publish:

@akofink Not related to this PR. You might need to do a db:migrate

[akofink]

Works as expected. ACK! Thanks @parthaa!