Add variant to dependency cycle errors

Use moduleInfo.String() to print dependency cycle errors so they
contain the variant.

Test: Test_parallelVisit
Change-Id: I2bddaa35c8abb57c42b4c424e861361a8813d588
diff --git a/context.go b/context.go
index ccf0409..f55b4b6 100644
--- a/context.go
+++ b/context.go
@@ -2158,9 +2158,8 @@
 	for i := len(cycle) - 1; i >= 0; i-- {
 		nextModule := cycle[i]
 		errs = append(errs, &BlueprintError{
-			Err: fmt.Errorf("    %q depends on %q",
-				curModule.Name(),
-				nextModule.Name()),
+			Err: fmt.Errorf("    %s depends on %s",
+				curModule, nextModule),
 			Pos: curModule.pos,
 		})
 		curModule = nextModule
diff --git a/context_test.go b/context_test.go
index 3e49a18..d91b89d 100644
--- a/context_test.go
+++ b/context_test.go
@@ -994,9 +994,9 @@
 			})
 		want := []string{
 			`encountered dependency cycle`,
-			`"C" depends on "A"`,
-			`"A" depends on "B"`,
-			`"B" depends on "C"`,
+			`module "C" depends on module "A"`,
+			`module "A" depends on module "B"`,
+			`module "B" depends on module "C"`,
 		}
 		for i := range want {
 			if len(errs) <= i {
@@ -1030,8 +1030,8 @@
 			})
 		want := []string{
 			`encountered dependency cycle`,
-			`"D" depends on "C"`,
-			`"C" depends on "D"`,
+			`module "D" depends on module "C"`,
+			`module "C" depends on module "D"`,
 		}
 		for i := range want {
 			if len(errs) <= i {
@@ -1067,8 +1067,8 @@
 			})
 		want := []string{
 			`encountered dependency cycle`,
-			`"G" depends on "F"`,
-			`"F" depends on "G"`,
+			`module "G" depends on module "F"`,
+			`module "F" depends on module "G"`,
 		}
 		for i := range want {
 			if len(errs) <= i {