Make random extension range configurable

Previously if subscriber was automatically created it got assigned
random MSISDN number between 20000 and 49999. Make it configurable with
new vty command "subscriber-create-on-demand random" and expand vty
tests to check it.

Change-Id: I040a1d227b0c7a1601dc7c33eccb0007941408a6
Related: OS#1658
diff --git a/openbsc/tests/db/db_test.c b/openbsc/tests/db/db_test.c
index ee0cbca..dc81481 100644
--- a/openbsc/tests/db/db_test.c
+++ b/openbsc/tests/db/db_test.c
@@ -164,7 +164,7 @@
 	struct gsm_subscriber *alice = NULL, *alice_db;
 	char scratch_str[256];
 
-	alice = db_create_subscriber(alice_imsi);
+	alice = db_create_subscriber(alice_imsi, GSM_MIN_EXTEN, GSM_MAX_EXTEN);
 	db_subscriber_assoc_imei(alice, imei1);
 	if (imei2)
 		db_subscriber_assoc_imei(alice, imei2);
@@ -217,7 +217,7 @@
 	struct gsm_subscriber *alice_db;
 
 	char *alice_imsi = "3243245432345";
-	alice = db_create_subscriber(alice_imsi);
+	alice = db_create_subscriber(alice_imsi, GSM_MIN_EXTEN, GSM_MAX_EXTEN);
 	db_sync_subscriber(alice);
 	alice_db = db_get_subscriber(GSM_SUBSCRIBER_IMSI, alice->imsi);
 	COMPARE(alice, alice_db);
@@ -228,7 +228,7 @@
 	test_subs("9993245423445", "1234567890", "6543560920");
 
 	/* create it again and see it fails */
-	alice = db_create_subscriber(alice_imsi);
+	alice = db_create_subscriber(alice_imsi, GSM_MIN_EXTEN, GSM_MAX_EXTEN);
 	OSMO_ASSERT(!alice);
 
 	test_sms();