Improve servinit generation in Docker containers #356

Job	Run time
Ubuntu (x86_64) release	1m 48s
Ubuntu (x86_64) debug	1m 1s
Windows (x86_64) release (crossbuild from Ubuntu x86_64, MinGW-w64)	2m 2s
macOS (x86_64) release	1m 27s
	6m 18s

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