Why installing openjdk-7-jdk on Ubuntu Trusty installs systemd as well?

[Yuri Kanivetsky]

By the way, the Ubuntu is running in lxc container. And untill I do
`apt update`, it doesn't want systemd to be installed. `systemd` pops
up after doing `apt update`. Before that `apt-cache policy` says:

# apt-cache policy openjdk-7-jdk
openjdk-7-jdk:
  Installed: (none)
  Candidate: 7u101-2.6.6-0ubuntu0.14.04.1
  Version table:
     7u101-2.6.6-0ubuntu0.14.04.1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ trusty-security/main
amd64 Packages
     7u51-2.4.6-1ubuntu4 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages