Description of problem:
Dracut should print out a URL that it is trying to download. Either do it every time before dracut tries to download something, or at least print it every time dracut fails to download something. That will greatly improving debugging in case something it wrong. Here's an example use case:

> [  OK  ] Started Show Plymouth Boot Screen.
> [  OK  ] Reached target Basic System.
> [    7.199730] 8139cp 0000:00:03.0: eth0: link up, 100Mbps, full-duplex, lpa 0x05E1
> [    7.202331] ip (344) used greatest stack depth: 5340 bytes left
> dracut-initqueue[279]: % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
> dracut-initqueue[279]: Dload  Upload   Total   Spent    Left  Speed
>   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0:--:-- --:--:--     0
> dracut-initqueue[279]: curl: (22) The requested URL returned error: 404 File not found
> dracut-initqueue[279]: Warning: can't find installer mainimage path in .treeinfo
> dracut-initqueue[279]: % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
> dracut-initqueue[279]: Dload  Upload   Total   Spent    Left  Speed
>   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0:--:-- --:--:--     0
> dracut-initqueue[279]: curl: (22) The requested URL returned error: 404 File not found
> dracut-initqueue[279]: Warning: Could not boot.
> dracut-initqueue[279]: RTNETLINK answers: File exists
> [  OK  ] Started Show Plymouth Boot Screen.
> [  OK  ] Reached target Basic System.
> dracut-initqueue[279]: % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
> dracut-initqueue[279]: Dload  Upload   Total   Spent    Left  Speed
>   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0:--:-- --:--:--     0
> dracut-initqueue[279]: curl: (22) The requested URL returned error: 404 File not found
> dracut-initqueue[279]: Warning: can't find installer mainimage path in .treeinfo
> dracut-initqueue[279]: % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
> dracut-initqueue[279]: Dload  Upload   Total   Spent    Left  Speed
>   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0:--:-- --:--:--     0
> dracut-initqueue[279]: curl: (22) The requested URL returned error: 404 File not found
> dracut-initqueue[279]: Warning: Could not boot.
> dracut-initqueue[279]: Warning: /dev/root does not exist
> [   43.640190] systemd-udevd (262) used greatest stack depth: 5260 bytes left
> 
> 
> Entering emergency mode. Exit the shell to continue.
> Type "journalctl" to view system logs.
> 
> dracut:/# 

After seeing this, I have no idea what dracut tried to download and therefore it's hard to guess whether there is a bug in dracut/anaconda, or I'm missing some important files on my web server.

(This is just an example for illustration, I know the core issue in this case).

If dracut prints the URL of at least the failed downloads, it will be much easier for the user to do something about it.

Version-Release number of selected component (if applicable):
F18 Alpha RC3

How reproducible:
always

Steps to Reproduce:
1. boot kernel+vmlinuz with inst.repo=http://server/path, where /path doesn't contain required files