HPCC-10930 Better support in regression suite for targeting specific queries

Implement
    - a handler to query a list of ECL files (with wildcards) in command line
    - a handler to execute multiple query like run a suite to generate
      final result and diff report
    - handler to use parallel execution for multiple ECL query files

Update README.rst and built-in help text.

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>