Support new command-line options to specify ID Certificate and private key

[ClarkTucker]

Sometimes it is useful to test with a different ID Certificate and corresponding private key.
Currently these values are 'hardcoded' in the vendors 'configurator' implementation.

I propose to add support for new command line options that would, if present, override the vendor default value for these security configuration items.

This could be implemented this way:

1. parsing the new command-line options;
2. passing the values (if provided) to the 'create_participant()' operation that is defined by each vendor implementation;
3. in the vendor specific code, check these parameters, and, if not 'empty', use them instead of the default values.

Alternatively, we could:

1. expose the default values from the vendor implementation;
2. parse the new command-line options if present, overriding the default values;
3. pass the values (either the defaults, or as parsed from command-line) to the create_participant() operation in the vendor specific header;
4. use the passed values in create_participant().

The second approach might simplify the vendor-specific code a little...