Admin password check works with yescrypt; shorter Blancco version warning

chpasswd and passwd write yescrypt ($y$) hashes, which the openssl $6$
comparison could not read: every re-run set the pxe password again, and a
box whose password was 'pxe' in yescrypt passed the pxe_admin_password
requirement. Both Admin tasks now compare with crypt(), which handles every
scheme. The config.img warning names the two Blancco versions instead of
the staging guard's merge instructions.

webapp/tests/test_share_accounts.py

@@ -190,7 +190,8 @@ class ShareAccounts(Fixture):
         with open(os.path.join(BU.blancco_root(), "config.img"), "wb") as f:
             f.write(cfg)
         done = SA.set_password("blancco", PW)
-        self.assertTrue(any("WARNING" in d and "config.img" in d for d in done), done)
+        self.assertTrue(any("WARNING" in d and "config.img (BIOS boot) is Blancco 7.15" in d
+                            and "older than our 7.20" in d for d in done), done)
         with open(BP.served_prefs_path(), "rb") as f:
             self.assertEqual(self.prefs_share_pw(f.read()), PW)
         with open(os.path.join(BU.blancco_root(), "config.img"), "rb") as f: