Add `erase_old_deployments` and run it during upgrades

[pbchase]

Add function, erase_old_deployments, to
upgrade.py. It should erase the "-previous" directories and the directories that are not suffixed with "-previous" separately. For each group it should search for directories that match the pattern env.backup_project_full_path*. It should keep N of each such directory where N is a passed parameter. N should default to 3.

Call this new function with a target directory of env.upload_target_backup_dir

redcap_deployment/upgrade.py

Line 28 in 602cb1d

online()

It is important that we call this function late in the upgrade process to assure the process has worked as well as can be assured.