`qubes-firewall.service` fails on `fedora-26-minimal` fails because of bad `qubes-core-agent` version

[SaswatPadhi]

Qubes OS version:

Qubes release 4.0 (R4.0)

Affected component(s):

Firewall service (qubes-core-agent) on fedora-26-minimal

---

Steps to reproduce the behavior:

1. Install fedora-26-minimal template
2. dnf update the template
3. Install dependencies for a NetVM
4. Use it as TemplateVM for sys-firwall
5. Restart sys-firewall
6. Run within sys-firewall: journalctl -u qubes-firewall.service -b

Expected behavior:

No errors in journal -- Qubes firewall updater runs without issues.

Actual behavior:

Mar 07 00:38:31 sys-firewall systemd[1]: Started Qubes firewall updater.
Mar 07 00:38:32 sys-firewall qubes-firewall[457]: Traceback (most recent call last):
Mar 07 00:38:32 sys-firewall qubes-firewall[457]:   File "/usr/sbin/qubes-firewall", line 6, in <module>
.
. . . <truncated> . . .
.
Mar 07 00:38:32 sys-firewall qubes-firewall[457]: pkg_resources.DistributionNotFound: The 'qubesagent==4.0.20' distribution was not found and is required by the application
Mar 07 00:38:32 sys-firewall systemd[1]: qubes-firewall.service: Main process exited, code=exited, status=1/FAILURE

General notes:

This issue does not arise on Fedora 26 image which has 4.0.20 version of qubes-core-agent. But Fedora 26 Minimal image has 4.0.24.