Add preliminary OEM UID/GID support.

Until we implement full support for passwd/group files, add a simple
way to use the new OEM UID/GID range (5000-5999).

oem_XXX -> 5000 + XXX iff 0 <= XXX < 1000.

Bug: 23225475

Change-Id: If48b88135d5df538313414f747d6c4c63bf0a103
diff --git a/tests/stubs_test.cpp b/tests/stubs_test.cpp
index 2d1bdee..c81ca58 100644
--- a/tests/stubs_test.cpp
+++ b/tests/stubs_test.cpp
@@ -122,6 +122,14 @@
   check_get_passwd("radio", 1001, TYPE_SYSTEM);
 }
 
+TEST(getpwnam, oem_id_0) {
+  check_get_passwd("oem_0", 5000, TYPE_SYSTEM);
+}
+
+TEST(getpwnam, oem_id_999) {
+  check_get_passwd("oem_999", 5999, TYPE_SYSTEM);
+}
+
 TEST(getpwnam, app_id_nobody) {
   check_get_passwd("nobody", 9999, TYPE_SYSTEM);
 }
@@ -247,6 +255,14 @@
   check_get_group("radio", 1001);
 }
 
+TEST(getgrnam, oem_id_0) {
+  check_get_group("oem_0", 5000);
+}
+
+TEST(getgrnam, oem_id_999) {
+  check_get_group("oem_999", 5999);
+}
+
 TEST(getgrnam, app_id_nobody) {
   check_get_group("nobody", 9999);
 }