Repolist improvements

[yoshiotu]

Currently you can create a file in $BANYAN_HOST_DIR/hostcollector/repolist with one namespace/repo on each line indicating repos for Collector to inspect. You can change the contents of the list on-the-fly and Collector will eventually read the updated list and process the new repos. A few improvements seem desirable:

• Read the updated file sooner, instead of first processing all images from the previous list of repos.
• Allow users to wildcard the repo field, e.g. banyanops/*

[yoshiotu]

Updated the code to read the repolist file more frequently, in particular it reads the file once each time it finishes processing a batch of 5 images.

Still need to implement wildcarding. In addition, it might be useful to limit the tag set for each repo.