Make preinstall.d more deterministic

Reorders the preinstall, making the order more explicit.  Also dedupes
some folder setup.

Change-Id: I423dcba169558ff6037a3382b997675722e77405

diskimage_builder/elements/gentoo/pre-install.d/02-gentoo-02-flags

@@ -6,8 +6,12 @@ fi
 set -eu
 set -o pipefail
 
-mkdir -p /etc/portage/package.use
+# get the directories in order
+mkdir -p /etc/portage/profile
 mkdir -p /etc/portage/package.keywords
+mkdir -p /etc/portage/package.mask
+mkdir -p /etc/portage/package.unmask
+mkdir -p /etc/portage/package.use
 
 # needed in order to install pip packages as root
 echo 'dev-python/pip vanilla' >> /etc/portage/package.use/pip

diskimage_builder/elements/gentoo/pre-install.d/02-gentoo-04-install-desired-python

@@ -18,11 +18,6 @@ if [[ ! -f /usr/portage/profiles ]]; then
     emerge-webrsync -q
 fi
 
-# get the directories in order
-mkdir -p /etc/portage/profile
-mkdir -p /etc/portage/package.keywords
-mkdir -p /etc/portage/package.use
-
 # python-3.6 and python-3.5 are masked and considered unstable for some reason
 echo "PYTHON_TARGETS=\"${GENTOO_PYTHON_TARGETS}\"" >> /etc/portage/make.conf
 if [[ "${GENTOO_PYTHON_TARGETS}" == *"python3_6"* ]]; then