One more buck replacements in onos-prepare-sonar

Change-Id: I93c43fa641d45fa007d0a379dd0ac5bd020594c9
diff --git a/tools/build/onos-prepare-sonar b/tools/build/onos-prepare-sonar
index bcef1d1..0b10168 100755
--- a/tools/build/onos-prepare-sonar
+++ b/tools/build/onos-prepare-sonar
@@ -97,8 +97,7 @@
   if tests:
     rmtree(path + '/surefire-reports', ignore_errors=True)
     rmtree('surefire-reports', ignore_errors=True)
-    runCmd(['buck',
-            'test',
+    runCmd([BUCK, 'test',
             '--no-cache', '--no-results-cache',
             '--code-coverage',
             '--no-results-cache',