Improve remote_test::test_notExistingCall()

Improve remote_test::test_notExistingCall()

There are actually 2 distinct test cases of invalid methods:

1. Not following the definition in Api class's PHPDoc block
   - core methods begin by a 'dokuwiki' or 'wiki' followed by a . and
     the method name itself.
   - plugin methods are formed like 'plugin.<plugin name>.<method name>'
2. Method "type" does not begin with 'dokuwiki', 'wiki' or 'plugin'

A new check was added so both are now covered.

Test was modified to make use of PHPUnit expectException() method,
instead of relying on a try/catch block.