Optionally remove portage files

Optionally remove portage files, so that we can cache package and
keep the portage directory around, specifically for nodepool.

This also adds a section to the Gentoo readme about the variable
and renames the 00-gentoo-distro-name environment file to a more
appropriate name of 00-gentoo-envars.

Also brought up was the location of the gentoo-releng.gpg file,
this has been moved and the refrencing paths updated.

Change-Id: I20c91b36082828faa1ca481585acc5f9933211e1

elements/gentoo/README.rst

@@ -30,3 +30,7 @@ Notes:
     default/linux/amd64/13.0/no-multilib
     hardened/linux/amd64
     hardened/linux/amd64/no-multilib
+
+* You can set the GENTOO_PORTAGE_CLEANUP environment variable to true (or
+  anything other than False) to clean up portage from the system and get the
+  image size smaller.

elements/gentoo/environment.d/00-gentoo-envars.bash

@@ -1,2 +1,3 @@
 export DISTRO_NAME=gentoo
 export GENTOO_PROFILE=${GENTOO_PROFILE:-'default/linux/amd64/13.0'}
+export GENTOO_PORTAGE_CLEANUP=${GENTOO_PORTAGE_CLEANUP:-'False'}

elements/gentoo/post-install.d/99-cleanup

@@ -23,8 +23,11 @@ shopt -s extglob
 rm -Rf /tmp/!(ccache|in_target*|profiledir*)
 shopt -u extglob
 
-rm -Rf /root/.ccache/* /usr/portage/* /usr/src/* /var/cache/edb/dep/* /var/cache/genkernel/* /var/empty/* /var/run/* /var/state/* /var/tmp/* /var/cache/portage/distfiles
+rm -Rf /root/.ccache/* /usr/src/* /var/cache/edb/dep/* /var/cache/genkernel/* /var/empty/* /var/run/* /var/state/* /var/tmp/*
 rm -Rf /etc/*- /etc/*.old /etc/ssh/ssh_host_* /root/.*history /root/.lesshst /root/.ssh/known_hosts /root/.viminfo /usr/share/genkernel /usr/lib64/python*/site-packages/gentoolkit/test/eclean/testdistfiles.tar.gz
+if [[ "${GENTOO_PORTAGE_CLEANUP}" != "False" ]]; then
+    rm -Rf /usr/portage/* /var/cache/portage/distfiles
+fi
 
 # shrink a bit
 for i in $(find /var/log -type f); do echo > $i; done

elements/gentoo/root.d/10-gentoo-image

@@ -33,8 +33,6 @@ if ! [ 'x86_64' = "${ARCH}" ] ; then
     exit 1
 fi
 
-# get the element location so we can refrence things relative to it
-ELEMENT_DIR=${ELEMENT_DIR:-"${ELEMENTS_PATH##*:}/gentoo"}
 # valid gentoo profiles are as follows
 # default/linux/amd64/13.0
 # default/linux/amd64/13.0/no-multilib
@@ -81,7 +79,7 @@ else
     # https://dev.gentoo.org/~dolsen/releases/keyrings/gentoo-keys-*.tar.xz
     # http://distfiles.gentoo.org/distfiles/gentoo-keys-*.tar.xz
     GPGDIR=$(mktemp -d -t)
-    gpg --no-default-keyring --keyring "${GPGDIR}"/gentookeys.gpg --import "${ELEMENT_DIR}"/gentoo-releng.gpg
+    gpg --no-default-keyring --keyring "${GPGDIR}"/gentookeys.gpg --import "${TMP_HOOKS_PATH}"/extra-data.d/gentoo-releng.gpg
     # check the sig file
     gpgv --keyring "${GPGDIR}"/gentookeys.gpg "${CACHED_SIGNATURE_FILE}"
     if [[ "${?}" != 0 ]]; then