Add portage support for Gentoo Linux (#1076)

Co-authored-by: Christopher Phillips <christopher.phillips@anchore.com>

test/cli/packages_cmd_test.go

@@ -96,7 +96,7 @@ func TestPackagesCmdFlags(t *testing.T) {
 			name: "squashed-scope-flag",
 			args: []string{"packages", "-o", "json", "-s", "squashed", coverageImage},
 			assertions: []traitAssertion{
-				assertPackageCount(33),
+				assertPackageCount(34),
 				assertSuccessfulReturnCode,
 			},
 		},

test/integration/catalog_packages_cases_test.go

@@ -277,6 +277,14 @@ var commonTestCases = []testCase{
 			"netbase": "5.4",
 		},
 	},
+	{
+		name:    "find portage packages",
+		pkgType: pkg.PortagePkg,
+		pkgInfo: map[string]string{
+			"app-containers/skopeo": "1.5.1",
+		},
+	},
+
 	{
 		name:        "find jenkins plugins",
 		pkgType:     pkg.JenkinsPluginPkg,

test/integration/test-fixtures/image-pkg-coverage/pkgs/var/db/pkg/app-containers/skopeo-1.5.1/CONTENTS

@@ -0,0 +1,13 @@
+dir /usr
+dir /usr/bin
+obj /usr/bin/skopeo 376c02bd3b22804df8fdfdc895e7dbfb 1649284374
+dir /etc
+dir /etc/containers
+obj /etc/containers/policy.json c01eb6950f03419e09d4fc88cb42ff6f 1649284375
+dir /etc/containers/registries.d
+obj /etc/containers/registries.d/default.yaml e6e66cd3c24623e0667f26542e0e08f6 1649284375
+dir /var
+dir /var/lib
+dir /var/lib/atomic
+dir /var/lib/atomic/sigstore
+obj /var/lib/atomic/sigstore/.keep_app-containers_skopeo-0 d41d8cd98f00b204e9800998ecf8427e 1649284375

test/integration/test-fixtures/image-pkg-coverage/pkgs/var/db/pkg/app-containers/skopeo-1.5.1/LICENSE

@@ -0,0 +1 @@
+Apache-2.0 BSD BSD-2 CC-BY-SA-4.0 ISC MIT

test/integration/test-fixtures/image-pkg-coverage/pkgs/var/db/pkg/app-containers/skopeo-1.5.1/SIZE

@@ -0,0 +1 @@
+27937835