sysrescue-autorun: improve type casting for booleans

The recently implemented type casting code doesn't work intuitively for
booleans: for example it treats a string "0" as False and doesn't show
an error message for it. So the user might be unaware of this.

So add a dedicated conversion function for booleans.

Also add checks for conversions from dicts and lists, forbid to cast them
to strings because that is most probably not what the user wants.

airootfs/etc/systemd/scripts/sysrescue-autorun

@@ -124,12 +124,36 @@ def search_autoruns(dirname, suffixes, copyfilefct):
             found+=1
     return found
 
+def strtobool (val):
+    """Convert a string representation of truth to true (1) or false (0).
+
+    True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
+    are 'n', 'no', 'f', 'false', 'off', and '0'.  Raises ValueError if
+    'val' is anything else.
+    
+    Function adapted from Pythons distutils.util.py because it will be deprecated soon
+    Copyright (c) Python Software Foundation; All Rights Reserved
+    """
+    val = str(val).lower()
+    if val in ('y', 'yes', 't', 'true', 'on', '1'):
+        return True
+    elif val in ('n', 'no', 'f', 'false', 'off', '0'):
+        return False
+    else:
+        raise ValueError("invalid truth value %r" % (val,))
+
 def read_cfg_value(name, defaultval):
     if name in config:
+        chkval = config[name]
         try:
-            val = type(defaultval)(config[name])
+            if isinstance(chkval, list) or isinstance(chkval, dict):
+                raise TypeError(f"must be a {type(defaultval)}, not a {type(chkval)}")
+            elif isinstance(defaultval, bool) and not isinstance(chkval, bool):
+                val = strtobool(chkval)
+            else:
+                val = type(defaultval)(chkval)
         except (TypeError, ValueError) as e:
-            writemsg(f"{name} with {config[name]} is not the same type as defaultval: {e}")
+            writemsg(f"config['{name}'] with {chkval} is not the same type as defaultval: {e}")
             val = defaultval
     else:
         val = defaultval