[JENKINS-20784] - Avoid user's creation in TriggeringUsersAuthorizationStrategy
Bad guys can insert everything to UserIdCause, so it is preferable to have such check.
Related to https://issues.jenkins-ci.org/browse/JENKINS-20784

Signed-off-by: Oleg Nenashev <nenashev@synopsys.com>
Merge pull request #2 from oleg-nenashev/userIdCause_Fix

[JENKINS-20784] - Avoid user's creation in TriggeringUsersAuthorizationStrategy