Spotted by ShellCheck.

geb authored Jul 06, 2020 and intrigeri committed Jul 21, 2020

As tails-spoof-mac is running as root, its messages cannot be translated
according to the user settings. This commit solves this problem by reading the
localization settings from the environment (/etc/default/locale) in
tails-spoof-mac initialization. To make this work, we also set up the desired
localization environment before launching tails-unblock-network and
tails-spoof-mac.

... and disable it by default.

We want to be able to persist the password file, so we can't delete it.
And since the password is now hashed and salted, we don't have to delete
it anymore.

By calling chpasswd with the -e option, it uses the provided hashed and
salted password instead of hashing and salting it via PAM.

PAM uses SHA512 to hash the password, as configured in /etc/login.defs,
so in the call to mkpasswd we set --method=sha512crypt to also use SHA512.

To make it easier to persist all of these settings.

Apply greeter-buster-blocking-tails-unblock-network.diff to the Greeter files now shipped here (refs: #16912)

Those are the files installed by the greeter, from the master branch of
the greeter repo (commit 2b1facdbe3c4c9f209cdcf3835a9d52a3147b8a8).

All files are copied to the same path they are installed at when
installing the greeter Debian package, except for:

 * The tailsgreeter Python package, which is now installed under
   /usr/local/lib/python3/ instead of /usr/lib/python3, because
   that's where we put our own Python packages.

 * The tails-greeter script, which is now installed in /usr/local/lib/
   instead of /usr/bin, because this script should not be executed by
   the user directly, similar to the other scripts in the lib directory.
   The Exec= path in tails-greeter.desktop is updated accordingly.