Test Congress Doctor driver support

Test Congress Doctor driver support

When running Congress as Inspector implementation, the Monitor has to be
started after starting the Inspector because we need to first ensure the
Doctor datasource is created, otherwise the Monitor cannot get the
Doctor datasource ID at init.

This patch defaults the Inspector to 'sample' and for the time being
functest will run only against 'sample',  not all supported Inspector
types ('sample' and 'congress'). Testing multiple Inspectors in single
functest run would require major additional changes to our test scripts.
It should still be done and addressed in a future patch. This patch
focus on adding testing support against Congress as first step.

One can test against Congress executing for example:
$ INSPECTOR_TYPE=congress INSTALLER_TYPE=local COMPUTE_HOST=compute1 ./run.sh

JIRA: DOCTOR-56

Change-Id: Icebd6fd6ad0c01d511c97e804727ad2a71f742e8
Signed-off-by: Carlos Goncalves <carlos.goncalves@neclab.eu>