Autocomplete for restoreconfig and clearconfig

Use complete_path from ui_backstore.

Signed-off-by: Andy Grover <agrover@redhat.com>
Catch exception if an invalid tag is given when creating a tpg

Also, allow e.g "tpg6" as well as "6" for the tpg tag. This matches what
we do for lun creation.

Fixes #47

Signed-off-by: Andy Grover <agrover@redhat.com>
Add a global pref for adding default portal

Expand info messages to mention this pref as well

Fixes #46

Signed-off-by: Andy Grover <agrover@redhat.com>