In case the plinth process is interrupted, the "finally" block that is
meant to unhold the package may not be executed, and the package will
stay held. The flag is used to indicate this situation, so it can be
resolved the next time apt_hold_freedombox is used.
Tests:
- (normal) No hold on freedombox package, and flag is not set. Install
any app. Afterwards, there is no hold, and flag is not set.
- (admin preference) Place hold on freedombox package, but flag is not
set. Install any app. Afterwards, there is still a hold, but flag is
not set.
- (recovery) Place hold on freedombox package, but flag is
set. Install any app. Afterwards, there is no hold, and flag is not
set.
Signed-off-by: James Valleroy <jvalleroy@mailbox.org>