systemd-journald fails to start on CentOS 7
The AVC indicates that the file being read doesn't have an SELinux label.
This can happen if SELinux was disabled when the file was created, or if it is created on a filesystem that isn't SELinux-capable (e.g. vfat).
If someone had disabled and re-enabed SELinux, then you should be able to fix the problem (and possibly many others) by relabeling the filesystem. You can do this online with:
restorecon -r /
If the filesystem on which the file resides doesn't support SELinux, then you need to replace it with a filesystem that does support SELinux, and then relabel.