CI: Output a summary using GITHUB_SUMMARY

Uses teststat to parse the go test json and output markdown which will
be posted as a summary to the github action run.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

Vagrantfile

@@ -227,6 +227,7 @@ EOF
         'RUNC_FLAVOR': ENV['RUNC_FLAVOR'] || "runc",
         'GOTEST': ENV['GOTEST'] || "go test",
         'GOTESTSUM_JUNITFILE': ENV['GOTESTSUM_JUNITFILE'],
+        'GOTESTSUM_JSONFILE': ENV['GOTESTSUM_JSONFILE'],
     }
     sh.inline = <<~SHELL
         #!/usr/bin/env bash