Set filecontext for the test apex

Label the surfaceflinger binary as surfaceflinger_exec

Test: m apex.test; m; device is bootable

Change-Id: I22297ba514f7ba298a1d0d4b476a447f26e48078
diff --git a/apex/apex.test-file_contexts b/apex/apex.test-file_contexts
index bd71a2a..3dffd86 100644
--- a/apex/apex.test-file_contexts
+++ b/apex/apex.test-file_contexts
@@ -1,2 +1,3 @@
 /manifest\.json   u:object_r:system_file:s0
 (/.*)?            u:object_r:system_file:s0
+/bin/surfaceflinger u:object_r:surfaceflinger_exec:s0