testsuite run the defrag latency test solo

this test is time sensitive and it sometimes fail to pass below the
latency threshold, even on strong machines.

this test was the reson we're running just 2 parallel tests in the
github actions CI, revering this.

.github/workflows/ci.yml

@@ -12,9 +12,9 @@ jobs:
     - name: test
       run: |
         sudo apt-get install tcl8.5
-        ./runtest --clients 2 --verbose
+        ./runtest --verbose
     - name: module api test
-      run: ./runtest-moduleapi --clients 2 --verbose
+      run: ./runtest-moduleapi --verbose
 
   build-ubuntu-old:
     runs-on: ubuntu-16.04