Fix for 17.04/17.10/18.04 Install failures

Problem definition:

Ever since 17.04 remastersys/PinguyBuilder/Forks fail to compete
the install process.

This is due to the change from Swap Partition to Swap File in 17.04.

The problem occurs because we are including the the swapfile created
by the initial install of Ubuntu/Flavors in the remaster which causes
errors in /lib/partman/finish.d/25create_swapfile and therefor the
install fails.

The fix:

The fix is to add "/swapfile" to the list of excluded files in the settings
dialog of PinguyBuilder under "Files to exclude".

In other words change "/windows /dos" to "/windows /dos /swapfile"

I have tested this in 18.04 on both a mini generated Unity respin(GTK)
as well as my 18.04 Plasma(e.g. KDE) respin. I also verified that the
newly created swapfile was present in the newly installed system and
showed up in "ls -lh/", cat /proc/swaps and the /etc/fstab file
(e.g. that is was correctly created and enabled).

Pinguy.. You may want to add this to /etc/PinguyBuilder.conf so it is
the default.

Hope this helps,
WolfLand