Parameterize /usr/libexec everywhere #4370

Job	Run time
checks (make -f Makefile fmt-ci, 1.74.0, rustfmt)	59s
checks (make -f Makefile fmt-ci, 1.74.0, rustfmt)	59s
checks_with_tang (TANG_URL=tang RUST_LOG=stratisd=debug make -f Makefile test-clevis-loop, 1.74.0...	12m 42s
checks_with_tang (TANG_URL=tang RUST_LOG=stratisd=debug make -f Makefile test-clevis-loop, 1.74.0...	12m 42s
checks (make -f Makefile check-typos, 1.74.0, cargo)	57s
checks (make -f Makefile check-typos, 1.74.0, cargo)	57s
python-based-tests	2m 25s
python-based-tests	2m 25s
shell-checks	38s
shell-checks	38s
stratis-cli-checks	9m 32s
stratis-cli-checks	9m 32s
stratis-min-cli-checks	2m 24s
stratis-min-cli-checks	2m 24s
tests-with-testing-repo (HEAD, --verify-sysfs)	25m 52s
tests-with-testing-repo (HEAD, --verify-sysfs)	25m 36s
tests-with-testing-repo (v3.6.0)	24m 39s
tests-with-testing-repo (v3.6.0)	24m 39s
	2h 40m 0s

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