libs/common: refactor libs/common 2 (#4231)

* libs/common: refactor libs/common 2

- move random function to there own pkg

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* change imports and usage throughout repo

* fix goimports

* add changelog entry

abci/example/kvstore/helpers.go

@@ -2,14 +2,14 @@ package kvstore
 
 import (
 	"github.com/tendermint/tendermint/abci/types"
-	cmn "github.com/tendermint/tendermint/libs/common"
+	"github.com/tendermint/tendermint/libs/rand"
 )
 
 // RandVal creates one random validator, with a key derived
 // from the input value
 func RandVal(i int) types.ValidatorUpdate {
-	pubkey := cmn.RandBytes(32)
-	power := cmn.RandUint16() + 1
+	pubkey := rand.RandBytes(32)
+	power := rand.RandUint16() + 1
 	v := types.Ed25519ValidatorUpdate(pubkey, int64(power))
 	return v
 }