Fix Podman client address resolution

[wagoodman]

This refactors some of the podman client address resolution logic such that:

• podman env vars override config files
• rootless socket is attempted first before trying the default socket
• uncomments and fixes the podman integration tests
• refactors the podman os actions to use the afero FS abstraction (makes testing easier for the new client tests)

[github-actions[bot]]

Benchmark Test Results

Benchmark results from the latest changes vs base branch

``` latest: Pulling from library/ubuntu tar: Option --mtime: Treating date 'UTC 2019-09-16' as 2019-09-16 00:00:00 goos: linux goarch: amd64 pkg: github.com/anchore/stereoscope/pkg/file cpu: Intel(R) Xeon(R) CPU E5-2673 v4 @ 2.30GHz docker: │ ./.tmp/benchmark-9450e9e.txt │ │ sec/op │ TarIndex-2 41.22µ ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ B/op │ TarIndex-2 5.560Ki ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ allocs/op │ TarIndex-2 93.00 ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 pkg: github.com/anchore/stereoscope/test/integration │ ./.tmp/benchmark-9450e9e.txt │ │ sec/op │ SimpleImage_GetImage/docker-archive-2 1.623m ± ∞ ¹ SimpleImage_GetImage/oci-archive-2 1.443m ± ∞ ¹ SimpleImage_GetImage/oci-dir-2 943.4µ ± ∞ ¹ geomean 1.302m ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ B/op │ SimpleImage_GetImage/docker-archive-2 331.4Ki ± ∞ ¹ SimpleImage_GetImage/oci-archive-2 645.8Ki ± ∞ ¹ SimpleImage_GetImage/oci-dir-2 413.1Ki ± ∞ ¹ geomean 445.5Ki ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ allocs/op │ SimpleImage_GetImage/docker-archive-2 2.840k ± ∞ ¹ SimpleImage_GetImage/oci-archive-2 1.570k ± ∞ ¹ SimpleImage_GetImage/oci-dir-2 1.354k ± ∞ ¹ geomean 1.821k ¹ need >= 6 samples for confidence interval at level 0.95 docker: Error response from daemon: Get "http://localhost/v2/": dial tcp [::1]:80: connect: connection refused. │ ./.tmp/benchmark-9450e9e.txt │ │ sec/op │ SimpleImage_FetchSquashedContents/docker-archive-2 16.68µ ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ B/op │ SimpleImage_FetchSquashedContents/docker-archive-2 2.648Ki ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 │ ./.tmp/benchmark-9450e9e.txt │ │ allocs/op │ SimpleImage_FetchSquashedContents/docker-archive-2 21.00 ± ∞ ¹ ¹ need >= 6 samples for confidence interval at level 0.95 ```