wheezy: fix persistence-setup which crashes while creating new persistence after creating

Fix Persistence-setup which crashes while creating new persistence after creating persistent container but before configuring it (Icon ‘seahorse-key’ not present in theme at /usr/share/perl5/Tails/Persistence/Configuration/Button.pm line 45.)

Parent Task: #6015 (closed)

Original created by @tails on 5420 (Redmine)

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