In verbose mode print a progress bar during downloads
Add a slowtest marker, disable these tests in Travis
Test omego upgrade directly in Travis

Also a couple of flake8 fixes
Fix a couple of ProgressBar errors
Add a resolver for multi-stage db upgrades
Use subprocess.call instead of Popen

in case we're running unzip and it prompts for an ovewrite
Fix arguments to run() in External.omero_bin and DbAdmin.psql