Define log callback function to use with libcryptsetup

Logs from libcryptsetup now go to stderr and this prevents issues like
the one reported in https://bugzilla.redhat.com/show_bug.cgi?id=1770395

luksmeta.c

@@ -45,6 +45,17 @@ struct options {
     int slot;
 };
 
+#define LUKSMETA_LIBCRYPTSETUP_LOG_LEVEL CRYPT_LOG_ERROR
+
+static void
+luksmeta_libcryptsetup_log(int level, const char *msg, void *usrptr)
+{
+    if (level != LUKSMETA_LIBCRYPTSETUP_LOG_LEVEL) {
+       return;
+    }
+    fprintf(stderr, "%s", msg);
+}
+
 static int
 cmd_test(const struct options *opts, struct crypt_device *cd)
 {
@@ -485,6 +496,8 @@ main(int argc, char *argv[])
             return EX_IOERR;
         }
 
+        crypt_set_log_callback(cd, luksmeta_libcryptsetup_log, NULL);
+
         r = crypt_load(cd, NULL, NULL);
         if (r != 0) {
             fprintf(stderr, "Unable to read LUKSv1 header (%s): %s\n",