Add unit tests for show commands on multi ASIC platform for per namespace output.

[smaheshm]

The "display" option will not work. Requires a bit of explanation but it has to do with 'multi-asic-click-options' which populates the parameters before the environment variables are set un 'setup()' method. Due to this the multi asic namespace options are not available when the pytest framework loads all the .py files. Tried several options including 'reload', but it didn't work. We are dicussing internally what other options are available including changing implementation of 'multi-asic-click-option'.

Can you include cases to cover all the options for 'show stats' and 'show config'. display for a namespace, display when a set of ports/queues are included?

Originally posted by @neethajohn in #1080 (comment)

[smaheshm]

added unit tests.