[JENKINS-58041] Add support for IPv6 when getting "Jenkins URL"<br><br>Default...

[JENKINS-58041] Add support for IPv6 when getting "Jenkins URL"<br><br>Default "Jenkins URL" do not support IPv6 address。<br>For example my Jenkins server address is "[http://[6000::24]:8080/jenkins"|http://[6000::24]:8080/jenkins]<br>But the default value of "Jenkins URL" in "Jenkins Location" Section of "Configuration System" webpage is: “http://[6000:8080/jenkins/”<br><br>We fixed the bug in Jenkins.getRootUrlFromRequest()