Use absolute file paths for compat testing

[mcvsubbu]

Compatibility tester needs that the yaml files used for testing (and the file paths within yaml files) reside in the resource directory path. We should change these so that the files can be absolute path. This will allow Pinot installations to specify their own test suite and run compat testing before upgrade to new pinot versions.

The tester script should take a directory name (absolute path) as the argument where all the yaml files are located. The yaml files should be named as pre-controller-upgrade.yaml, pre-broker-upgrade.yaml, etc (6 of them) . The shell script should be modified to pick up these yaml files from the directory specified.

In addition, the directory should contain a subdir called config under which all the config file names should reside (e.g. the table config files, schema files, kafka producer config files. etc.), possibly under subdirectories if the user chooses to put them that way. These config files are the ones referenced inside the yaml files.

So ,if a yaml file referes to a table config file as mytables/table1.conf, then we should look in the directory ${TOPLEVELDIR}/config/mytables/table1.conf in order to retrieve the table config file.