Description of problem:
With a limited amount of storage on a Satellite 6.1 server, it would be good to have a mechanism built in to the sync process which checks available disk space and errors or produces a warning before starting the download. As the syncs are carried asynchronously, this could be carried out on a per-repo basis?

Version-Release number of selected component (if applicable): 6.1

How reproducible:
Spin up a test Sat6 server with limited storage (/var ~10 Gb perhaps)

Steps to Reproduce:
1. Install & build Sat6.
2. Enable RHEL5, 6, & 7 Repos
3. Start sync process

Expected results: Once the metadata has been processed there would be (I assume?) a rough idea of how much is to be downloaded per repo. If this is larger than available in /var/lib/pulp, the produce a warning.

Additional info: