test: Fix race condition in avocado checklogin-basic.py
test: Fix race condition in avocado checklogin-basic.py

The test was missing the `wait_visible("#login")` after the second
opening of the `/system` page. Move it to the `login()` helper function
instead  to avoid repetition.

moraleslazaro/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,petervo/cockpit,cockpit-project/cockpit,andreasn/cockpit,Scribery/cockpit,mareklibra/cockpit,deryni/cockpit,andreasn/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,mareklibra/cockpit,deryni/cockpit,garrett/cockpit,stefwalter/cockpit,Scribery/cockpit,stefwalter/cockpit,cockpit-project/cockpit,andreasn/cockpit,stefwalter/cockpit,cockpituous/cockpit,mvollmer/cockpit,petervo/cockpit,stefwalter/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,mareklibra/cockpit,mvollmer/cockpit,petervo/cockpit,Scribery/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,SotolitoLabs/cockpit,cockpituous/cockpit,cockpit-project/cockpit,stefwalter/cockpit,cockpit-project/cockpit,petervo/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,mareklibra/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,petervo/cockpit,petervo/cockpit,stefwalter/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,petervo/cockpit,mvollmer/cockpit,deryni/cockpit,cockpituous/cockpit,andreasn/cockpit,cockpit-project/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,deryni/cockpit,mareklibra/cockpit,deryni/cockpit,andreasn/cockpit,garrett/cockpit,cockpituous/cockpit,garrett/cockpit,andreasn/cockpit,Scribery/cockpit