[1.7.x] Fixed #22791 -- Invoke interactive questioner only for conflicts in specified apps.

Thanks bendavis78 for the report and Tim Graham for the review.

Backport of f7a78f9bba from master

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0001_initial.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    operations = [
+
+        migrations.CreateModel(
+            "Author",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("name", models.CharField(max_length=255)),
+                ("slug", models.SlugField(null=True)),
+                ("age", models.IntegerField(default=0)),
+                ("silly_field", models.BooleanField(default=False)),
+            ],
+        ),
+
+        migrations.CreateModel(
+            "Tribble",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("fluffy", models.BooleanField(default=True)),
+            ],
+        )
+
+    ]

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0002_conflicting_second.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("unspecified_app_with_conflict", "0001_initial")]
+
+    operations = [
+
+        migrations.CreateModel(
+            "Something",
+            [
+                ("id", models.AutoField(primary_key=True)),
+            ],
+        )
+
+    ]

tests/migrations/migrations_test_apps/unspecified_app_with_conflict/migrations/0002_second.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("unspecified_app_with_conflict", "0001_initial")]
+
+    operations = [
+
+        migrations.DeleteModel("Tribble"),
+
+        migrations.RemoveField("Author", "silly_field"),
+
+        migrations.AddField("Author", "rating", models.IntegerField(default=0)),
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+            ],
+        )
+
+    ]