bots: Use a more efficient way to get GitHub statuses
bots: Use a more efficient way to get GitHub statuses

Looks like we were repetetively trying to retrieve information
about statuses in an inefficient manner. We just need the latest
status for each context.

https://developer.github.com/v3/repos/statuses/#get-the-combined-status-for-a-specific-ref

Closes #6703

SotolitoLabs/cockpit,petervo/cockpit,andreasn/cockpit,larskarlitski/cockpit,andreasn/cockpit,andreasn/cockpit,stefwalter/cockpit,garrett/cockpit,mareklibra/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,michalskrivanek/cockpit,dperpeet/cockpit,mareklibra/cockpit,martinpitt/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,deryni/cockpit,dperpeet/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,cockpit-project/cockpit,larsu/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,Scribery/cockpit,moraleslazaro/cockpit,larsu/cockpit,michalskrivanek/cockpit,martinpitt/cockpit,larsu/cockpit,cockpit-project/cockpit,michalskrivanek/cockpit,larskarlitski/cockpit,SotolitoLabs/cockpit,mvollmer/cockpit,dperpeet/cockpit,stefwalter/cockpit,petervo/cockpit,larskarlitski/cockpit,stefwalter/cockpit,michalskrivanek/cockpit,xhad/cockpit,larskarlitski/cockpit,mvollmer/cockpit,andreasn/cockpit,mareklibra/cockpit,andreasn/cockpit,dperpeet/cockpit,deryni/cockpit,harishanand95/cockpit,mvollmer/cockpit,mvollmer/cockpit,deryni/cockpit,dperpeet/cockpit,cockpituous/cockpit,mareklibra/cockpit,cockpit-project/cockpit,harishanand95/cockpit,larsu/cockpit,xhad/cockpit,petervo/cockpit,moraleslazaro/cockpit,michalskrivanek/cockpit,xhad/cockpit,harishanand95/cockpit,larskarlitski/cockpit,michalskrivanek/cockpit,Scribery/cockpit,stefwalter/cockpit,mareklibra/cockpit,Scribery/cockpit,dperpeet/cockpit,petervo/cockpit,Scribery/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,cockpit-project/cockpit,harishanand95/cockpit,xhad/cockpit,cockpituous/cockpit,martinpitt/cockpit,martinpitt/cockpit,Scribery/cockpit,larsu/cockpit,andreasn/cockpit,moraleslazaro/cockpit,petervo/cockpit,garrett/cockpit,xhad/cockpit,michalskrivanek/cockpit,deryni/cockpit,Scribery/cockpit,mvollmer/cockpit,deryni/cockpit,petervo/cockpit,garrett/cockpit,dperpeet/cockpit,xhad/cockpit,deryni/cockpit,larskarlitski/cockpit,moraleslazaro/cockpit,deryni/cockpit,mareklibra/cockpit,cockpituous/cockpit,garrett/cockpit,xhad/cockpit,larskarlitski/cockpit,cockpituous/cockpit,cockpit-project/cockpit,martinpitt/cockpit,harishanand95/cockpit,stefwalter/cockpit,petervo/cockpit,cockpituous/cockpit,Scribery/cockpit,harishanand95/cockpit,SotolitoLabs/cockpit,harishanand95/cockpit,garrett/cockpit,larsu/cockpit