Fix ownership on artifact copies

Summary:
The implementation of D984 did not include enforcing ownership for
`build.CopyFrom` instruction and so artifacts copied from one image to
another via `copies:` were problematically owned as root.

In order to fix this behavior:
 1. `config.ArtifactConfig` `build.CopyFrom` instructions are now
    injected duration `build.PhaseInstall`
 2. `config.VariantConfig` calls `build.ApplyUser` for these artifact
    instructions as well using the `runs.as` user
 3. `build.CopyAs` was refactored to wrap any `build.Instruction` which
    should only really be used with `build.Copy` or `build.CopyFrom`.

Test Plan:
Run `go test ./...`. Run `blubber` against configuration with a variant that
uses `copies` and verify that the `COPY --from` instructions also include a
`--chown` flag.

Reviewers: thcipriani, mmodell, hashar, #release-engineering-team, demon

Reviewed By: thcipriani, #release-engineering-team

Tags: #release-engineering-team

Differential Revision: https://phabricator.wikimedia.org/D1002

1 files changed, 19 insertions, 3 deletions

diff --git a/build/instructions_test.go b/build/instructions_test.go
index 29508e2..77938dd 100644
--- a/build/instructions_test.go
+++ b/build/instructions_test.go
@@ -37,9 +37,25 @@ func TestCopy(t *testing.T) {
 }
 
 func TestCopyAs(t *testing.T) {
-	i := build.CopyAs{123, 124, build.Copy{[]string{"source1", "source2"}, "dest"}}
-
-	assert.Equal(t, []string{"123:124", `"source1"`, `"source2"`, `"dest"`}, i.Compile())
+	t.Run("wrapping Copy", func(t *testing.T) {
+		i := build.CopyAs{
+			123,
+			124,
+			build.Copy{[]string{"source1", "source2"}, "dest"},
+		}
+
+		assert.Equal(t, []string{"123:124", `"source1"`, `"source2"`, `"dest"`}, i.Compile())
+	})
+
+	t.Run("wrapping CopyFrom", func(t *testing.T) {
+		i := build.CopyAs{
+			123,
+			124,
+			build.CopyFrom{"foo", build.Copy{[]string{"source1", "source2"}, "dest"}},
+		}
+
+		assert.Equal(t, []string{"123:124", "foo", `"source1"`, `"source2"`, `"dest"`}, i.Compile())
+	})
 }
 
 func TestCopyFrom(t *testing.T) {