[2.7] bpo-34155: Dont parse domains containing @ (GH-13079) (GH-16006)

[2.7] bpo-34155: Dont parse domains containing @ (GH-13079) (GH-16006)

This change skips parsing of email addresses where domains include a "@" character, which can be maliciously used since the local part is returned as a complete address.

(cherry picked from commit 8cb65d1381b027f0b09ee36bfed7f35bb4dec9a9)

Excludes changes to Lib/email/_header_value_parser.py, which did not
exist in 2.7.

Co-authored-by: jpic <jpic@users.noreply.github.com>
https://bugs.python.org/issue34155