Share accounts: an older live Blancco release warns instead of failing

A fresh server gets boot-tools/blancco from the USB, which can be an older
Blancco (7.15.1) than our preferences (7.20). The version guard refused to
patch its config.img and the exception failed the whole share apply, so the
first-boot playbook failed. refresh_live_prefs() now returns a warning for
config.img and still writes the served preferences.xml (UEFI path).

webapp/services/share_accounts.py

@@ -177,7 +177,9 @@ def _apply_menu(password):
 
 def _apply_blancco():
     from services import blancco_update as bu
-    return "Blancco preferences: " + ("updated" if bu.refresh_live_prefs() else "unchanged")
+    changed, warning = bu.refresh_live_prefs()
+    out = "Blancco preferences: " + ("updated" if changed else "unchanged")
+    return out + (f" (WARNING: {warning})" if warning else "")
 
 
 def apply(only=None, values=None):