Version defaulting

[seanpearsonuk]

By default, the launch function should try to launch the latest installed version of Fluent (greatest value of the AWP root index).

[RebelYoung]

issue #1268
This is my problem for the lastest launcher.py.
It is not good for catch my version in the work station.

[RebelYoung]

I test the command in two virtual enviroments, both version 0.11.0 and 0.12.1,
launch_fluent works in previous one.

in left py38f11 has the version 0.11.0 package.

[mkundu1]

We shall have the following 3 options to specify Fluent launch path from PyFluent:

1. default - via AWP_ROOT env vars
2. user override - via the product_version param in launch_fluent
3. developer override - via PYFLUENT_FLUENT_ROOT env var

Other options are redundant and will be removed.

[seanpearsonuk]

We shall have the following 3 options to specify Fluent launch path from PyFluent:

1. default - via AWP_ROOT env vars
2. user override - via the product_version param in launch_fluent
3. developer override - via PYFLUENT_FLUENT_ROOT env var

Other options are redundant and will be removed.

This will be a positive change. Thanks, @mkundu1.