Filter out the special PXE boot parameters

[lslezak]

Problem

• The special PXE boot parameters are passed to the installed system, that's wrong
• The special PXE boot parameters are copied to the installed system #2280

Solution

• Enhance the filtering code to ignore the specific PXE boot parameters
• Remove also most of the network settings

Testing

• The unit test has been updated
• Tested manually

Screenshots

After booting the installer via PXE the extra parameters can be seen in the /proc/cmdline file. But the /run/agama/cmdline.d/kernel.conf does not include them and the journal log shows they were ignored:

After booting the installed system no PXE boot option is present on the linux line:

[jreidinger]

well, to be sure I would enhance test with various parameters we are using like some rd.kiwi params and some oh others which are more tricky to be sure that regexp matching

[lslezak]

BTW using spaces in parameters does not work properly. e.g. initrd="/boot/ /initrd" is not processed correctly.

We use a simple shell word splitting functionality, for proper parsing we would need to write our full parser and process the input character by character. That's not trivial and then we would probably need to fix all code which uses the processed /run/agama/cmdline.d/kernel.conf file.

Using spaces or newlines in file names usually causes troubles. I'd keep it as it is and fix it only when we get a real use case for this scenario.

[ancorgs]

LGTM