broker: refactor bootstrap block

Problem: the code block that selects which boot method to use
is not very clear.

Simplify code block so that the default path is clear and
adding a boot method won't increase complexity.

Author: garlick

src/broker/broker.c

@@ -200,7 +200,6 @@ int main (int argc, char *argv[])
     struct sigaction old_sigact_term;
     flux_msg_handler_t **handlers = NULL;
     const flux_conf_t *conf;
-    const char *method;
     flux_error_t error;
 
     memset (&ctx, 0, sizeof (ctx));
@@ -340,24 +339,23 @@ int main (int argc, char *argv[])
     init_attrs_starttime (ctx.attrs, ctx.starttime);
 
     /* Execute broker network bootstrap.
-     * Default method is pmi.
-     * If [bootstrap] is defined in configuration, use static configuration.
      */
-    if (attr_get (ctx.attrs, "broker.boot-method", &method, NULL) < 0) {
+    const char *boot_method;
+    if (attr_get (ctx.attrs, "broker.boot-method", &boot_method, NULL) < 0) {
         if (flux_conf_unpack (conf, NULL, "{s:{}}", "bootstrap") == 0)
-            method = "config";
+            boot_method = "config";
         else
-            method = NULL;
+            boot_method = NULL;
     }
-    if (!method || !streq (method, "config")) {
-        if (boot_pmi (ctx.overlay, ctx.attrs) < 0) {
-            log_msg ("bootstrap failed");
+    if (boot_method && streq (boot_method, "config")) {
+        if (boot_config (ctx.h, ctx.overlay, ctx.attrs) < 0) {
+            log_msg ("boot-config failed");
             goto cleanup;
         }
     }
     else {
-        if (boot_config (ctx.h, ctx.overlay, ctx.attrs) < 0) {
-            log_msg ("bootstrap failed");
+        if (boot_pmi (ctx.overlay, ctx.attrs) < 0) {
+            log_msg ("boot-pmi failed");
             goto cleanup;
         }
     }