fedup-cli fails if not run as user w/ superuser privileges

[tflink]

After installing fedup, it is possible to run fedup-cli as a non-root user without using sudo. If this happens, all the packages are downloaded without issue but right after the upgrade transaction is tested, the following error message shows up:

testing upgrade transaction
rpm transaction 100% [=========================================================================================]
rpm install 100% [=============================================================================================]
setting up system for upgrade
Traceback (most recent call last):
  File "/usr/bin/fedup-cli", line 179, in <module>
    main(args)
  File "/usr/bin/fedup-cli", line 167, in main
    prep_upgrade(pkgs, bootloader=args.bootloader)
  File "/usr/lib/python2.7/site-packages/fedup/download.py", line 211, in prep_upgrade
    link_pkgs(pkgs)
  File "/usr/lib/python2.7/site-packages/fedup/download.py", line 141, in link_pkgs
    os.mkdir(packagedir, 0755)
OSError: [Errno 13] Permission denied: '/var/lib/fedora-upgrade'

I was able to re-run fedup-cli using sudo and it completed without issue.

fedup should probably check for privileges before starting in order to avoid this error

[tflink]

Another side effect of not checking is that adding a non-standard repo fails when running as non-root with no error message about privileges - I had to hack in a log message to figure out why it was failing

[wgwoods]

I left that out intentionally because I was going to use polkit to get privs rather than just a dumb "hey are you root?" check at the start.

Obviously, time is running a bit short for that. I'll add the stupid check now and do the polkit stuff later.