Translate password field placeholder in Checkout

[mimarcel]

Description

Translate placeholder

Manual testing scenarios

1. Open Guest Mode browsing
2. Go to checkout
3. Enter the email address of a customer which already exists

Expected:
Placeholder is translated.

Actual:
Placeholder is not translated.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)