[gdb/testsuite] Improve gdb.testsuite/quotemeta.exp

Improve test-case gdb.testsuite/quotemeta.exp by:
- catching errors in check_quotemeta
- logging argument and results of calling quotemeta using verbose -log
- renaming quotemeta_fail to check_quotemeta_fail for consistency with
  check_quotemeta
- reducing escaping using {}
- adding a missing test checking "@bad-name"