.gitignore: some temporary directories created by packer

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Retool provisioning scripts how I want 'em

o Adds configurable "cpus" and "memory" settings which
  a) Affect parallelism during ebuilds during the packaging
     process
  b) Carry over into the resulting virtual machines

o Keep more remnants of the kernel build around so that
  down the line a mere "emerge gentoo-sources" will suffice
  (perhaps sometimes even that is not neccesary) to satisfy
  ebuilds and provide accurate information about the
  real kernel

o Provide a bit more status reporting during the packaging process

o Make sure the package database is consistent (even for TYPE=virtualbox
  builds) when we run emerge --depclean by removing the kernel packages,
  and temporarily setting them as "package.provided" during --depclean.

o Use <<-EOF instead of <<'EOF' heredoc convention in scripts for
  enhanced readability

o export variables explicitly in provision.sh rather than relying on
  dubious implicit exportation from packer.

o add vim

o double the disk space to 120G

o double the default RAM provisioning to 1G

o on vmware boxes, set "guest_os_type" to "other3xlinux-64" (which I
  suspect is a magical name, although I haven't double-checked this
  actually works tbh).

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>