backend: always log copr-builder-ready std{out,err}

[praiskup]

Complements: #3426

[FrostyX]

FTR output looks like this for Fedora:

[2024-10-17 10:36:36,861][  INFO][PID:4107598] Checking that builder machine is OK
[2024-10-17 10:36:37,023][  INFO][PID:4107598] stdout:
Red Hat subscription not needed for fedora-40-x86_64
Builder is ready to be used

[2024-10-17 10:36:37,024][  INFO][PID:4107598] stderr:
(empty)

And RHEL:

[2024-10-17 10:36:37,023][  INFO][PID:4107600] Checking that builder machine is OK
[2024-10-17 10:36:37,522][  INFO][PID:4107600] stdout:
Checking Red Hat subscription (attempt #1)
Red Hat subscription active
Builder is ready to be used

[2024-10-17 10:36:37,525][  INFO][PID:4107600] stderr:
(empty)

[praiskup]

Ok, closing.