remove: Base._cleanup
remove: Base.localPackages
remove: dnf.yum.misc.re_remote_url()
runTransaction(): clean_used_packages() should run after verify_transaction()
Handle remote URLs. (RhBug:1030297)

Set the tempfile extension to ".rpm", add_cmdline_package() needs that.
Unlink tempfiles after the transaction has run unless keepcache was set.