AccountApi: Add method to add email address to account

Change I27a538d5b upgraded commons-validator to make sure that
email addresses like "user@example.systems" are recognized as
valid.

That change was added on stable-2.11 and there are no tests that
confirm that it works as expected.

Extend the Accounts API with a simple method to add a new email
address to an account, with a test case to confirm that it works
as expected.

Change-Id: I3ff4488f07a2a1e568308df62ea05a8c5a2e9408
3 files changed