[FIXED JENKINS-24475] - Properly handle UsernameNotFoundException on impersonation

This change allows to avoid non-existent users introduced since 1.564.1.
The change also handles a possible issue in OwnershipAuthorizeProjectStrategy.

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Code refactoring

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Refactoring - solve FindBugs notifications

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Merge pull request #27 from synopsys-arc-oss/JENKINS-24475

[JENKINS-24475] and refactoring