resource: exclude: remove unnecessary use of flux_log_error()

Problem: When inventory_targets_to_ranks() fails, flux_log_error() is
used, even though a textual error is already available in error.text.

Use flux_log() instead to avoid useless strerror() string appended
to error message.

Update one test that expected the sterror.

Author: grondo

src/modules/resource/exclude.c

@@ -64,10 +64,11 @@ struct exclude *exclude_create (struct resource_ctx *ctx,
         if (!(exclude->idset = inventory_targets_to_ranks (ctx->inventory,
                                                            exclude_idset,
                                                            &error))) {
-            flux_log_error (ctx->h,
-                            "error decoding exclude set %s: %s",
-                            exclude_idset,
-                            error.text);
+            flux_log (ctx->h,
+                      LOG_ERR,
+                      "error decoding exclude set %s: %s",
+                      exclude_idset,
+                      error.text);
             goto error;
         }
         if (idset_count (exclude->idset) > 0

t/t2315-resource-system.t

@@ -107,7 +107,7 @@ test_expect_success 'invalid exclude hosts cause instance failure' '
 	test_must_fail flux start -s 2 \
 		-o,--config-path=$(pwd)/${name},-Slog-filename=${name}/logfile \
 		flux resource list -s up -no {nnodes} > ${name}/nnodes &&
-    grep "nosuchhost: Invalid argument" ${name}/logfile
+    grep "invalid hosts: nosuchhost" ${name}/logfile
 '
 
 test_expect_success 'gpu resources in configured R are not verified' '