[Enhancement] Specify VCS output executable instead of simv for parallel runs

[amal-khailtash]

Using pytest-xdist or pytest-parallel would not work with single generated simv. Specifying a different work_dir does not seem to work either.

Having a way to separate VCS runs (output to a different directory) or a different name for simv would solve this issue.

[themperek]

Something like this? https://github.com/themperek/cocotb-test/blob/b992e3c3c7644f8581811cd2ca6a01d23f2115b3/tests/test_parameters.py#L53-L54

sim_buld specify where it will be compiled.

[amal-khailtash]

I guess I was confused between work_dir and sim_build. That could work, but if I wanted to create all tests in the same directory, this would not let me do that. Still a good work around. Thanks.