internal/pkg: optional executable files

This enables a FileArtifact implementation to specify whether its resulting file should be executable. This change also implements shebang and ELF magic checks in the file artifact.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/daemon_test.go

@@ -63,7 +63,7 @@ func TestNoReply(t *testing.T) {
 	}
 
 	<-done
-	wantIdent := pkg.MustDecode("fRn1L_pE6JbizdDOKS9GiZXEIp_yx4YYz_nSuv423hGnxAI2rUAwnR1OG1zjsP0N")
+	wantIdent := pkg.MustDecode("bpVsJ69hdKPBntMh_u777g7-quFNVmMlBJQOlM_thiQa9JnOFLAbe5OlR4zNjZ32")
 	if gotIdent := c.Ident(a).Value(); gotIdent != wantIdent {
 		t.Errorf(
 			"cureFromIR: %s, want %s",
@@ -124,7 +124,7 @@ func TestDaemon(t *testing.T) {
 	cancel()
 	<-done
 
-	const want = "fRn1L_pE6JbizdDOKS9GiZXEIp_yx4YYz_nSuv423hGnxAI2rUAwnR1OG1zjsP0N"
+	const want = "bpVsJ69hdKPBntMh_u777g7-quFNVmMlBJQOlM_thiQa9JnOFLAbe5OlR4zNjZ32"
 	if got := filepath.Base(p.String()); got != want {
 		t.Errorf("cureRemote: %s, want %s", got, want)
 	}
@@ -132,7 +132,7 @@ func TestDaemon(t *testing.T) {
 	wantLog := []string{
 		"",
 		"daemon: aborting all pending cures",
-		"daemon: attempting to cancel invalid artifact C0YO8fkKg38JGK95j8k1tHywA7nMk9xp2TUa69di7uFvnKioTdOOLaDRiwRcs1Nf",
+		"daemon: attempting to cancel invalid artifact 58Vy_5beLZCvZX__KzRKyIE6vATleaZP1ZBxbqoWnekz9aZ1zkxNgcIUFI5V1_Jf",
 		"daemon: fulfilled artifact " + want,
 	}
 	gotLog := strings.Split(buf.String(), "\n")