gdb/testsuite: adjust yet another add-inferior test for native-extended-gdbserver board

I'm seeing this FAIL with the native-extended-gdbserver board:

    (gdb) add-inferior^M
    [New inferior 2]^M
    Added inferior 2 on connection 1 (extended-remote localhost:2365)^M
    (gdb) FAIL: gdb.python/py-parameter.exp: test_per_inferior_parameters: add-inferior

This is another case of add-inferior producing more output when
connected to a remote target.  Adjust the regexp to accomodate it.

Change-Id: Ic5760ff66712c54b90b9debf379dcbf6e07f6eeb