add chain name variable instead of parity default value

[branciard]

Name is hardcoded in the script here so when setting a custom name different from "parity" (the default name) the start will fail.

• docker-compose up OK with default name = parity

./parity-deploy.sh --config aura

• docker-compose up KO with key missing in Keys path /home/parity/data/keys/customName

./parity-deploy.sh --config aura --name customName

~/parity-deploy$ docker-compose up
Starting host1 ... done
Attaching to host1
host1    | Loading config file from /home/parity/authority.toml
host1    | 2019-03-19 13:47:37 UTC Starting Parity-Ethereum/v2.3.6-stable-7aab6b7-20190319/x86_64-linux-gnu/rustc1.33.0
host1    | 2019-03-19 13:47:37 UTC Keys path /home/parity/data/keys/customName
host1    | 2019-03-19 13:47:37 UTC DB path /home/parity/data/chains/customName/db/2b60f78822e95081
host1    | 2019-03-19 13:47:37 UTC State DB configuration: fast
host1    | 2019-03-19 13:47:37 UTC Operating mode: active
host1    | Consensus signer account not found for the current chain. You can create an account via RPC, UI or `parity account new --chain /home/parity/spec.json --keys-path /home/parity/data/keys`.

because the key is not generate at the right place.

This commit replace --dir $DEST_DIR/parity by --dir $DEST_DIR/$CHAIN_NAME and solve this problem.