3291 follow-up (#3323)

* changelog: use issue number instead of PR number

* follow up to #3291

- rpc/test/helpers.go add StopTendermint(node) func
- remove ensureDir(filepath.Dir(walFile), 0700)
- mempool/mempool_test.go add type cleanupFunc func()

* cmd/show_validator: wrap err to make it more clear

blockchain/store_test.go

@@ -22,7 +22,8 @@ import (
 	tmtime "github.com/tendermint/tendermint/types/time"
 )
 
-// A cleanupFunc cleans up any config / test files created for a particular test.
+// A cleanupFunc cleans up any config / test files created for a particular
+// test.
 type cleanupFunc func()
 
 // make a Commit with a single vote containing just the height and a timestamp