Bridge should stop if json keystore file is invalid

[rstormsf]

NFO:bridge:   using RPC connection
WARN:ethstore::accounts_dir::disk: Invalid key file: "keys/authority.json" (ErrorImpl { code: Message("Invalid hash"), line: 1, column: 111 })
WARN:ethstore::accounts_dir::disk: Invalid key file: "keys/authority.json" (ErrorImpl { code: Message("Invalid hash"), line: 1, column: 111 })
INFO:bridge: Acquiring home & foreign chain ids
INFO:bridge: Home chain ID: 77 Foreign chain ID: 42
INFO:bridge: Deploying contracts (if needed)
INFO:bridge: Loaded database
INFO:bridge: Starting listening to events
INFO:bridge::bridge: Retrieved home contract balance
INFO:bridge::bridge: Retrieved foreign contract balance

bridge should be stopped if keystore is missing/invalid