When using e.g. GitLab as container registry, the token name may be the
username. However, the token name can contain special characters
including spaces breaking the registry login like this:
Apr 25 15:35:48 test42 pre-start[294091]: image doesn't exist locally and login failed
Apr 25 15:35:52 test42 pre-start[294289]: Error: accepts at most 1 arg(s), received 2
Apr 25 15:35:52 test42 pre-start[294297]: Error: registry.example.com/foo/bar/baz: image not known
Applying `escapeShellArg` on it fixes the problem.
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