Use setuid as non-root user when in Docker

[zmughal]

This allows for building and testing code as a non-root user which is how most code will be run. Furthermore, certain code does not run as the root user for security reasons (e.g., sandboxed Chromium which requires --no-sandbox to run under a root user).

Connects with https://github.com/oberth-manoeuvre/p5-Oberth-Launch/issues/45.

[coveralls]

Pull Request Test Coverage Report for Build 77

• 19 of 19 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.2%) to 68.108%

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Totals
Change from base Build 72:	3.2%
Covered Lines:	126
Relevant Lines:	185

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💛 - Coveralls