This commit fixes regexp in order to detect mandatory long arguments
with hyphen like '--foo-bar <foo-bar>'.
Note that https://review.openstack.org/#/c/496189/ fixes the bug
paritally but it does not cover all cases.
Closes-Bug: #1706311
Co-Authored-By: Akihiro Motoki <amotoki@gmail.com>
Change-Id: I52b9fdecbf1abea1f819b0061fd80b7ca6e0906d