Add proper support for inspect of v1 image manifest

[estesp]

Fixes: #74

Fix the v1 image fetch to properly list layers for inspect.

Signed-off-by: Phil Estes [email protected]

[estesp]

Verifying correct output now for the example in #74:

$ ./manifest-tool inspect golang@sha256:7cf1f7ccf392bd834eb91f02892f48992d3c2ba292c2198315a4637bb9454c30
golang@sha256:7cf1f7ccf392bd834eb91f02892f48992d3c2ba292c2198315a4637bb9454c30: manifest type: application/vnd.docker.distribution.manifest.v1+json
      Digest: sha256:7cf1f7ccf392bd834eb91f02892f48992d3c2ba292c2198315a4637bb9454c30
Architecture: arm64
          OS: linux
    # Layers: 6
      layer 1: digest = sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4
      layer 2: digest = sha256:72f16051d572a3d5090dd2a64004d8b3b2736e4f64cb17f3e92dca899af50b41
      layer 3: digest = sha256:955cc90a48f73e8ddb4103727fc7761eb73961aa8d097bcd956ef6e4c3adae37
      layer 4: digest = sha256:8c00b1d46f4493b4bfe8c94c6226da7c7c76820ecc2f4b70e6a482d4fdaaca34
      layer 5: digest = sha256:7809c1a4c8e2fd286895f69d067b1a68841f9311a5c0e1afc51e64e57d777919
      layer 6: digest = sha256:3b00a3925ee4b356facd24aea8ece58982a66577023cb3596ce3a321aef976f9