Python script fixes and improvements

[Googulator]

• Support specifying size of the virtual disk for qemu
• For bare metal, only create a minimal sized boot disk image
• Don't create external.img, unless it's actually needed
• Use truncate() for extending disk images to the desired size (faster than writing zeros)
• Make source_manifest.py work again
• Make -qr compatible with kernel bootstrap (will need fix in kexec-fiwix to actually use more memory)
• Use correct partition alignment (only in the Python scripts yet, move_disk.sh needs to be also fixed)
• Reserve the first 1GB on boot disks (again, needs to be done in move_disk.sh too)
• Fix bootstrap.cfg creation/cleanup (broken by residual sysa reference)
• Avoid including a truncated copy of the srcfs image in itself
• Print the correct paths to the images in bare metal mode
• Rework source manifest generation to be based on the bootstrap manifest
• Support predownloading only the sources that are needed before network
• Eliminate steps/pre-network-sources, decide based on the bootstrap manifest instead

[fosslinux]

Could you please also;

• fix pylint errors
• squash any "Fix" commits that fix an error introduced in an earlier commit (within this PR) into that commit

[Googulator]

Is there a better way to do that in Git than redoing the entire series by hand, and force-pushing? I.e. something similar to Mercurial's histedit.

[fosslinux]

Is there a better way to do that in Git than redoing the entire series by hand, and force-pushing? I.e. something similar to Mercurial's histedit.

git rebase -i HEAD~n, where n is the number of commits back you'd like to adjust the history. Happy to walk you through this on IRC, give me a ping