check gdb.lookup_type return value in gdb.python/py-lookup-type.exp

check gdb.lookup_type return value in gdb.python/py-lookup-type.exp

This further improves this testcase to check the output of
our calls to gdb.lookup_type.

gdb/ChangeLog:

        * gdb.python/py-lookup-type.exp (test_lookup_type): Change
        the second test to print the name attribute of value
        returned by the call to gdb.lookup_type, and adjust
        the expected output accordingly.