Fixes nasa/fprime#2654

[LeStarch]

Related Issue(s)
Has Unit Tests (y/n)
Documentation Included (y/n)

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Change Description

Fixes nasa/fprime#2654:

1. Only check port availability if "server"
2. Trap OSError and recast as ValueError per expected check_arguments API

Future Work

This type of error isn't so much an "argument error" as it is a "runtime error". We should allow check_arguments to produce two types of exceptions one that is an argument error and prints help, the other that just prints the error.