在Ubuntu 18.04 LTS中安装Jenkins失败(无法启动LSB：启动时启动Jenkins.)

[症状]

>使用官方步骤安装Jenkins,但失败并显示错误消息无法启动LSB：在启动时启动Jenkins.
>重现步骤

wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add -
sudo apt-add-repository "deb https://pkg.jenkins.io/debian-stable binary/"
sudo apt install jenkins

>控制台日志

gaspar@jenkins:~$sudo apt install jenkins
...
Setting up default-jre-headless (2:1.9-62ubuntu2) ...
Setting up jenkins (2.107.2) ...
Job for jenkins.service Failed because the control process exited with error code.
See "systemctl status jenkins.service" and "journalctl -xe" for details.
invoke-rc.d: initscript jenkins,action "start" Failed.
● jenkins.service - LSB: Start Jenkins at boot time
   Loaded: loaded (/etc/init.d/jenkins; generated)
   Active: Failed (Result: exit-code) since Thu 2018-04-19 10:03:05 UTC; 9ms ago
     Docs: man:systemd-sysv-generator(8)
  Process: 27282 ExecStart=/etc/init.d/jenkins start (code=exited,status=7)
Apr 19 10:03:03 evt-jenkins systemd[1]: Starting LSB: Start Jenkins at boot time...
Apr 19 10:03:03 evt-jenkins jenkins[27282]:  * Starting Jenkins Automation Server jenkins
Apr 19 10:03:03 evt-jenkins su[27313]: Successful su for jenkins by root
Apr 19 10:03:03 evt-jenkins su[27313]: + ??? root:jenkins
Apr 19 10:03:03 evt-jenkins su[27313]: pam_unix(su:session): session opened for user jenkins by (uid=0)
Apr 19 10:03:03 evt-jenkins su[27313]: pam_unix(su:session): session closed for user jenkins
Apr 19 10:03:05 evt-jenkins jenkins[27282]:    ...fail!
Apr 19 10:03:05 evt-jenkins systemd[1]: jenkins.service: Control process exited,code=exited status=7
Apr 19 10:03:05 evt-jenkins systemd[1]: jenkins.service: Failed with result 'exit-code'.
Apr 19 10:03:05 evt-jenkins systemd[1]: Failed to start LSB: Start Jenkins at boot time.
dpkg: error processing package jenkins (--configure):
 installed jenkins package post-installation script subprocess returned error exit status 1
...

[环境]

> Ubuntu 18.04 LTS Beta2
>jenkins2.107.2

[根本原因]

> Ubuntu 18.04 LTS使用Java 9作为默认java
> Jenkins 2.107.2仍然使用Java 8

[解]

>在安装Jenkins之前安装Java 8

sudo add-apt-repository ppa:webupd8team/java
sudo apt install oracle-java8-installer
wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add -
sudo apt-add-repository "deb https://pkg.jenkins.io/debian-stable binary/"
sudo apt install jenkins