Support dot in usernames

[mgolshan]

Description

A brief summary describing the changes in this pull request. See JENKINS-XXXXX for further information.

Submitter checklist

• [ ] Link to JIRA ticket in description, if appropriate.
• [ ] Change is code complete and matches issue description
• [ ] Automated tests have been added to exercise the changes
• [ ] Reviewer's manual test instructions provided in PR description. See Reviewer's first task below.

Reviewer checklist

• [ ] Run the changes and verify that the change matches the issue description
• [ ] Reviewed the code
• [ ] Verified that the appropriate tests have been written or valid explanation given

Documentation changes

• [ ] Link to jenkins.io PR, or an explanation for why no doc changes are needed

Users/aliases to notify