tools/scylla-nodetool: repair: set the jobThreads request parameter

Although ScyllaDB ignores this request parameter, the Java nodetools
sets it, so it is better to have the native one do the same for
symmetry. It makes testing easier.
Discovered with the more strict request matching introduced in the next
patches.

test/nodetool/test_repair.py

@@ -478,6 +478,11 @@ def test_repair_unused_options(request, nodetool, jobs, full):
     if full:
         args.append(full)
 
+    if jobs:
+        job_threads = jobs[1]
+    else:
+        job_threads = "1"
+
     res = nodetool(*args, expected_requests=[
         expected_request("GET", "/storage_service/keyspaces", response=["ks"]),
         JMX_COLUMN_FAMILIES_REQUEST,
@@ -492,7 +497,7 @@ def test_repair_unused_options(request, nodetool, jobs, full):
                 "incremental": "false",
                 "pullRepair": "false",
                 "primaryRange": "false",
-                "jobThreads": "1"},
+                "jobThreads": job_threads},
             response=1),
         expected_request("GET", "/storage_service/repair_async/ks", params={"id": "1"}, response="SUCCESSFUL")])