Add MM Auth test; add auth_action_str() function

Add basic MM Authentication test setup, with fake DB access and RAND_bytes().

So far implement simple tests for IO error during DB access and missing auth
entry.

To print the auth action during tests, add struct auth_action_names and
auth_action_str() inline function in auth.[hc].
diff --git a/openbsc/src/libmsc/auth.c b/openbsc/src/libmsc/auth.c
index 65a9b03..8512316 100644
--- a/openbsc/src/libmsc/auth.c
+++ b/openbsc/src/libmsc/auth.c
@@ -31,6 +31,15 @@
 
 #include <stdlib.h>
 
+const struct value_string auth_action_names[] = {
+#define AUTH_ACTION_STR(X) { X, #X }
+	{ -1, "(internal error)" }, /* soon to be fixed with an enum val */
+	AUTH_ACTION_STR(AUTH_NOT_AVAIL),
+	AUTH_ACTION_STR(AUTH_DO_AUTH_THEN_CIPH),
+	AUTH_ACTION_STR(AUTH_DO_CIPH),
+	AUTH_ACTION_STR(AUTH_DO_AUTH),
+#undef AUTH_ACTION_STR
+};
 
 static int
 _use_xor(struct gsm_auth_info *ainfo, struct gsm_auth_tuple *atuple)