fix 2 errors when running p2p tests more than once

Error #1:

```
Error response from daemon: network with name local_testnet already exists
```

Fixed by stopping and removing local_testnet containers and removing
the network

Error #2:

```
docker: Error response from daemon: Conflict. The name "/test_container_basic" is already in use by container a7cd15d479a964675e7f259de4ed852e7dfef85b447514728f437cd0b980a709. You have to remove (or rename) that container to beable to reuse that name..
```

Fixed by adding `--rm` flag.

test/p2p/client.sh

@@ -8,7 +8,7 @@ CMD=$4
 
 echo "starting test client container with CMD=$CMD"
 # run the test container on the local network
-docker run -t \
+docker run -t --rm \
 	-v $GOPATH/src/github.com/tendermint/tendermint/test/p2p/:/go/src/github.com/tendermint/tendermint/test/p2p \
 	--net=$NETWORK_NAME \
 	--ip=$(test/p2p/ip.sh "-1") \

test/p2p/local_testnet_stop.sh

@@ -0,0 +1,12 @@
+#! /bin/bash
+set -u
+
+NETWORK_NAME=$1
+N=$2
+
+for i in `seq 1 $N`; do
+  docker stop local_testnet_$i
+  docker rm local_testnet_$i
+done
+
+docker network rm $NETWORK_NAME

test/p2p/test.sh

@@ -7,8 +7,13 @@ N=4
 
 cd $GOPATH/src/github.com/tendermint/tendermint
 
+# stop the existing testnet and remove local network
+set +e
+bash test/p2p/local_testnet_stop.sh $NETWORK_NAME $N
+set -e
+
 # start the testnet on a local network
-bash test/p2p/local_testnet.sh $DOCKER_IMAGE $NETWORK_NAME $N
+bash test/p2p/local_testnet_start.sh $DOCKER_IMAGE $NETWORK_NAME $N
 
 # test basic connectivity and consensus
 # start client container and check the num peers and height for all nodes