Enforce "Basic" UI when using --info switch

Blinkenlights does not work well (at all) when using the --info
switch. All we really want here is an output that can be pasted as
debugging information.

Enforce the usage of the "Basic" ui, when the --info switch is used.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

Changelog.draft.rst

@@ -21,6 +21,7 @@ Changes
 
 * Slight performance enhancement uploading mails to an IMAP server in the
   common case.
+* Enforce basic UI when using the --info switch
 
 Bug Fixes
 ---------

offlineimap/init.py

@@ -200,6 +200,7 @@ class OfflineImap:
             # TODO, make use of chosen ui for logging
             logging.warning('Using old interface name, consider using one '
                             'of %s' % ', '.join(UI_LIST.keys()))
+        if options.diagnostics: ui_type = 'basic' # enforce basic UI for --info
         try:
             # create the ui class
             self.ui = UI_LIST[ui_type.lower()](config)