make trust-plugin a separate module

skip cmd/docker-trust in tests, as it's a separate module.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.github/workflows/test.yml

@@ -71,7 +71,7 @@ jobs:
       -
         name: Test
         run: |
-          go test -coverprofile=/tmp/coverage.txt $(go list ./... | grep -vE '/vendor/|/e2e/')
+          go test -coverprofile=/tmp/coverage.txt $(go list ./... | grep -vE '/vendor/|/e2e/|/cmd/docker-trust')
           go tool cover -func=/tmp/coverage.txt
         working-directory: ${{ env.GOPATH }}/src/github.com/docker/cli
         shell: bash