cockpit.print: Fix kwargs parsing

.rpartition() will try to break this:

    foo="bar=baaz"

on the second equals sign instead of the first.  Change it to
.partition().

src/cockpit/print.py

@@ -168,10 +168,10 @@ def main():
         func = getattr(printer, command[0])
 
         for param in command[1:]:
-            left, _, right = param.rpartition('=')
+            left, eq, right = param.partition('=')
 
             # Does that look like a kwarg?
-            if left.replace('-', '_').isidentifier():
+            if eq and left.replace('-', '_').isidentifier():
                 key = left
                 param = right
             else: