Fix bogus gdb_test invocations

Fix bogus gdb_test invocations

A following patch will make gdb_test error out if bogus arguments are
passed, which exposed bugs in a few testcases:

 - gdb.python/py-parameter.exp, passing a spurious "1" as extra
   parameter, resulting in:

   ERROR: Unexpected arguments: {set test-file-param bar.txt} {The name of the file has been changed to bar.txt} {set new file parameter} 1

 - gdb.python/py-xmethods.exp, a missing test message, resulting in
   the next gdb_test being interpreted as message, question and
   response!  With the enforcing patch, this was caught with:

   ERROR: Unexpected arguments: {p g.mul<char>('a')} {From Python G<>::mul.*} gdb_test {p g_ptr->mul<char>('a')} {From Python G<>::mul.*} {after: g_ptr->mul<char>('a')}

 - gdb.base/pointers.exp, missing a quote.

Change-Id: I66f2db4412025a64121db7347dfb0b48240d46d4