Prevent zombie processes and properly handle Ctrl+C on bk docker #304

Job	Run time
unit-tests	1s
local-edit-tests	47s
stark.com/foo (linux)	46s
unavailable	17s
toolchain.com (linux)	25s
pyapp.com/pip (linux)	1m 7s
pyapp.com/poetry (linux)	25s
stark.com/foo@1.2.3 (linux)	28s
git-clone.com (linux)	26s
pc-cmake.com (linux)	25s
fix-machos.com (linux)	21s
version-transformer.com (linux)	51s
stark.com/foo (mac)	44s
toolchain.com (mac)	24s
pyapp.com/pip (mac)	58s
pyapp.com/poetry (mac)	56s
stark.com/foo@1.2.3 (mac)	36s
git-clone.com (mac)	48s
pc-cmake.com (mac)	20s
fix-machos.com (mac)	13s
version-transformer.com (mac)	1m 2s
	12m 20s

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