VTY tests: fill DB before running test

Create a test_subscriber.vty.sql file with a dummy entry that has the
ID 100. All entries created in test_subscriber.vty have an ID > 100
now. This will be used in follow-up commit [1] to create a database
entry with an invalid IMEI value to test the related error handling
code path (that entry could not be created through the VTY).

[1]: change-id I1af7b573ca2a1cb22497052665012d9c1acf3b30
     "VTY: integrate IMEI"

Related: OS#3733
Change-Id: I48a3a503d7ca96798e2d5f70429b5fc36393420e
diff --git a/tests/test_subscriber.vty.sql b/tests/test_subscriber.vty.sql
new file mode 100644
index 0000000..ff167aa
--- /dev/null
+++ b/tests/test_subscriber.vty.sql
@@ -0,0 +1,3 @@
+-- Dummy entry with ID=100 gives all subscribers created in the VTY test an
+-- ID > 100, so we can pre-fill the database with IDs < 100.
+INSERT INTO subscriber (id, imsi) VALUES(100, '000000000000100');