skip shutting down container cache if Docker was never used (#16951)
skip shutting down container cache if Docker was never used (#16951)

Skip shutting down the Docker container cache if Docker was never initialized in the first place.

[ci skip-build-wheels]
benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants