Description of problem:
There is no built-in facility to use dnf to see the changelogs/release notes for all available package updates

Version-Release number of selected component (if applicable):
dnf-1.1.10-3.fc25

How reproducible:
100% reproducible

Steps to Reproduce:
1. run `dnf check-update` and see that there are updates
2. Be struck with the desire to read the changelogs/release notes for these updates to see what you'd actually be installing
3. Go looking for a flag you can pass to `dnf updateinfo info` that will show the changelogs/release notes for all available package updates

Actual results:
There is no such flag. Instead, I have to hack up something myself:
dnf updateinfo info `dnf check-update | cut -d '.' -f 1 | xargs`


Expected results:
I can do something like `dnf updateinfo info --showAll`