Client API: introduce non-iteractive mode

Avoid blocking waiting for a user response when a program needs some
input from a user but it runs completely without user interaction.

Related to rhbz#1018297

Signed-off-by: Jakub Filak <jfilak@redhat.com>
ask for missing configuration instead of dying

These programs are mainly intended to be used by humans, so they should
be user friendly.

Related to rhbz#1018297

Signed-off-by: Jakub Filak <jfilak@redhat.com>
rephrase a message for missing configuration

Closes rhbz#1018297

Signed-off-by: Jakub Filak <jfilak@redhat.com>