add -rf when remove db in regression test

Summary:
force remove db dir when rebuilding
Closes https://github.com/facebook/rocksdb/pull/2067

Differential Revision: D4811926

Pulled By: lightmark

fbshipit-source-id: ab068a2

tools/regression_test.sh

@@ -131,7 +131,7 @@ function main {
           run_db_bench "fillseqdeterministic" $NUM_KEYS 1 0
       elif [[ ! -d $DB_PATH ]] || [[ "$(( $(date +"%s") - $(stat -c "%Y" $DB_PATH) ))" -gt "604800"  ]]; then
           echo "Rebuilding DB..."
-          rm $DB_PATH
+          rm -rf $DB_PATH
           run_db_bench "fillseqdeterministic" $NUM_KEYS 1 0
       fi
       DB_PATH=$tmp