Increase token size to 32 bytes

This fix bumps the token size from 16 to 32 bytes in order
to match the default minimum entropy as recommended by Python
docs.

Note, that there is also a comparison to a constant TOKEN_ΜΙΝ_LEN
where one module assumed that length to be characters and another
module (utils.py) assumes that length to be bytes. So this fix
uses bytes as the meaning from now on.

Fixes canonical#4481

Signed-off-by: Eric Brown <eric_wade_brown@yahoo.com>

scripts/wrappers/add_token.py

@@ -145,7 +145,7 @@ def print_short(token, check):
     parser.add_argument(
         "--token",
         "-t",
-        help="Specify the bootstrap token to add, must be 32 characters long. "
+        help="Specify the bootstrap token to add, must be 32 bytes long. "
         "Auto generates when empty.",
     )
     parser.add_argument(
@@ -163,10 +163,10 @@ def print_short(token, check):
     if args.token is not None:
         token = args.token
     else:
-        token = token_hex(16)
+        token = token_hex(32)
 
     if len(token) < TOKEN_ΜΙΝ_LEN:
-        print("Invalid token size.  It must be 32 characters long.")
+        print("Invalid token size.  It must be 32 bytes long.")
         exit(1)
 
     add_token_with_expiry(token, cluster_tokens_file, ttl)