self.comm is now set in BaseSolver

[eirikurj]

Purpose

With recent addition of self.comm to BaseSolver in baseclasses (see mdolab/baseclasses#29) self.comm will is overwritten.
However, PR mdolab/baseclasses#30 now adds self.comm as an argument to BaseSolver making it clear to the user where self.comm is set and less error-prone.
This PR adjusts the code to the above changes.

Type of change

What types of change is it?
Select the appropriate type(s) that describe this PR

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Checklist

Put an x in the boxes that apply.

• I have run flake8 and black to make sure the code adheres to PEP-8 and is consistently formatted
• I have run unit and regression tests which pass locally with my changes
• I have added new tests that prove my fix is effective or that my feature works
• I have added necessary documentation