bash-completion: new completion from scratch (RhBug:1070902)

Features:
  `--enablerepo`:
    completes by disabled repos (`dnf repolist disabled`)
  `--disablerepo`:
    completes by enabled repos (`dnf repolist enabled`)
  `install|update`:
    completes by available pkgs and if local path used (e.g. `./`),
    completes from local files which ends with `.rpm`
  `help`:
    complete only one command. I.e. `help help<TAB><TAB>` will complete
    nothing
  All options/args generates automatically

Used Elad Alfassa <elad@fedoraproject.org> code for completing
`install`, `remove|erase`, `update`, `info` commands.

Reference: https://bugzilla.redhat.com/show_bug.cgi?id=1070902