Bug 1400714

Description of problem:
Yum has this option `--setopt=alwaysprompt=no` to suppress some prompting. As expected, dnf understands this option as well but when using it, dnf fails with a Python exception.

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


How reproducible:
always

Steps to Reproduce:
1. make sure that xonsh isn't installed
2. dnf install --setopt=alwaysprompt=no xonsh
3.

Actual results:
Last metadata expiration check: 2:52:44 ago on Thu Dec  1 20:28:10 2016.
Dependencies resolved.
================================================================================
 Package                     Arch        Version              Repository   Size
================================================================================
Installing:
 python3-ply                 noarch      3.8-2.fc25           fedora      108 k
 python3-prompt_toolkit      noarch      1.0.0-2.fc25         fedora      402 k
 python3-setproctitle        x86_64      1.1.9-4.fc25         fedora       20 k
 python3-wcwidth             noarch      0.1.6-4.fc25         fedora       30 k
 xonsh                       noarch      0.4.6-1.fc25         fedora      994 k

Transaction Summary
================================================================================
Install  5 Packages

Total download size: 1.5 M
Installed size: 11 M
Traceback (most recent call last):
  File "/usr/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.5/site-packages/dnf/cli/main.py", line 174, in user_main
    errcode = main(args)
  File "/usr/lib/python3.5/site-packages/dnf/cli/main.py", line 60, in main
    return _main(base, args)
  File "/usr/lib/python3.5/site-packages/dnf/cli/main.py", line 120, in _main
    ret = resolving(cli, base)
  File "/usr/lib/python3.5/site-packages/dnf/cli/main.py", line 149, in resolving
    base.do_transaction(display=displays)
  File "/usr/lib/python3.5/site-packages/dnf/cli/cli.py", line 199, in do_transaction
    if self._promptWanted():
  File "/usr/lib/python3.5/site-packages/dnf/cli/cli.py", line 552, in _promptWanted
    for txmbr in self.tsInfo.getMembers():
  File "/usr/lib/python3.5/site-packages/dnf/util.py", line 79, in __getattr__
    % (C.__name__, name))
AttributeError: 'Base' object has no attribute 'tsInfo'

Expected results:
Just the installation of xonsh with its dependencies and without any prompting. 

In case something 'bad' happens that normally would require a prompt - e.g. a non-imported gpg key, a failed package verification - the command shouldn't continue with the install and abort.

Additional info:
It seems that the dnf manual doesn't document the `alwaysprompt` option, yet. At least I couldn't find it in http://dnf.readthedocs.io/en/latest/conf_ref.html