Data directory can't be specified in config

[dboreham]

Although the Libra home dir path can be specified for subcommands such as validator-init it appears the data directory is hard-wired here. Should be possible to also specify the location of the data directory.

A side effect of this is that validator-init appears to end up ignoring --path at least in part because the data dir is used as the base for the config elsewhere in validator_dialogue()