Tweak PXE boot test to also check kickstart file path
    
    One of the test cases we didn't yet automate is:
    https://fedoraproject.org/wiki/QA:Testcase_Kickstart_File_Path_Ks_Cfg
    Now we have a PXE test, it's actually a good opportunity to test
    that at the same time. I don't usually like combining tests like
    this but in this case it sort of makes sense as otherwise we'd
    have to have a whole parallel PXE install just to test this one
    other detail. So, instead of doing an interactive PXE install as
    we did at first, let's tweak the test to include a kickstart in
    the initramfs and run the install from that.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>