This lets you adjust the vary_r tunable on a per-rule basis.
Reflects ceph.git commit 
f944ccc20aee60a7d8da7e405ec75ad1cd449fac.
Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
        CRUSH_RULE_SET_CHOOSELEAF_TRIES = 9, /* override chooseleaf_descend_once */
        CRUSH_RULE_SET_CHOOSE_LOCAL_TRIES = 10,
        CRUSH_RULE_SET_CHOOSE_LOCAL_FALLBACK_TRIES = 11,
+       CRUSH_RULE_SET_CHOOSELEAF_VARY_R = 12
 };
 
 /*
 
                                choose_local_fallback_retries = curstep->arg1;
                        break;
 
+               case CRUSH_RULE_SET_CHOOSELEAF_VARY_R:
+                       if (curstep->arg1 >= 0)
+                               vary_r = curstep->arg1;
+                       break;
+
                case CRUSH_RULE_CHOOSELEAF_FIRSTN:
                case CRUSH_RULE_CHOOSE_FIRSTN:
                        firstn = 1;