Package hash tests fail on GH CI server

[c0c0n3]

At the moment, the test task of the GitHub CI workflow errors out on the package hash tests. Find out why exactly and fix the tests accordingly.

Details

I thought the reason for that was that after checking out the repo on a Linux box (during the CI workflow) the timestamps of the files we package up in the tests would be different each time, so the package hash would be too. That is, even if the files that make up the package are always the same, their mod/change/access time can be different at different times. Besides a fresh check out, this could also happen e.g. when merging a branch, opening one of the files locally, etc.

So I've implemented a fix to try making reproducible package hashes in our test cases by setting the mod/change/access time to the epoch's start. (That obviously entailed making the tgz lib more flexible to cater for that.) The approach/fix works fine on my macOS box (TM) but for some obscure reason it breaks on the Linux CI's.

Failed test run output

go test ./... -coverprofile cover.out
?   	github.com/martel-innovate/osmops	[no test files]
?   	github.com/martel-innovate/osmops/controllers	[no test files]
ok  	github.com/martel-innovate/osmops/osmops/cfg	0.007s	coverage: 99.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/engine	0.012s	coverage: 100.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/nbic	0.027s	coverage: 99.5% of statements
--- FAIL: TestPackOpenLdapNs (0.00s)
    build_pkg_test.go:96: want hash: cae[45](https://github.com/martel-innovate/osmops/runs/7957977761?check_suite_focus=true#step:7:46)06d23753ee95f21faf8c6f97eaa; got: 2767580693666c3cfdfd8c758b902b80
--- FAIL: TestPackOpenLdapKnf (0.00s)
    build_pkg_test.go:96: want hash: 95389ba9b38e9a76b66789217a178e75; got: b2173e707f1f5900e196e6b4db2de4f6
--- FAIL: TestPackOpenLdapNested (0.00s)
    build_pkg_test.go:96: want hash: 5c2c2e459d0997fbef089[49](https://github.com/martel-innovate/osmops/runs/7957977761?check_suite_focus=true#step:7:50)9a7976812; got: 0f1f6290a11dc100b3fa4[50](https://github.com/martel-innovate/osmops/runs/7957977761?check_suite_focus=true#step:7:51)130d59372
FAIL
coverage: 100.0% of statements
FAIL	github.com/martel-innovate/osmops/osmops/pkgr	0.012s
ok  	github.com/martel-innovate/osmops/osmops/util	0.003s	coverage: 100.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/util/bytez	0.005s	coverage: 100.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/util/file	0.017s	coverage: 98.4% of statements
ok  	github.com/martel-innovate/osmops/osmops/util/http	0.006s	coverage: 100.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/util/http/sec	0.007s	coverage: 100.0% of statements
ok  	github.com/martel-innovate/osmops/osmops/util/tgz	0.017s	coverage: 100.0% of statements
FAIL