Changes:
- Add VAULT_KV_MOUNT env var (default: kv) to make KV mount configurable
- Update hvault_kv_get to use ${VAULT_KV_MOUNT}/data/${path}
- Update hvault_kv_put to use ${VAULT_KV_MOUNT}/data/${path}
- Update hvault_kv_list to use ${VAULT_KV_MOUNT}/metadata/${path}
- Update tests to use kv/ paths instead of secret/
This ensures agents can read/write secrets using the same mount point
that the Nomad+Vault migration policies grant ACL for.