if ANSIBLE_VAULT_PASSWORD_FILE is set, 'ansible-vault rekey myvault.yml'
will fail to prompt for the new vault password file, and will use
None.
Fix is to split out 'ask_vault_passwords' into 'ask_vault_passwords'
and 'ask_new_vault_passwords' to make the logic simpler. And then
make sure new_vault_pass is always set for 'rekey', and if not, then
call ask_new_vault_passwords() to set it.
ask_vault_passwords() would return values for vault_pass and new
vault_pass, and vault cli previously would not prompt for new_vault_pass
if there was a vault_pass set via a vault password file.
Fixes#18247