Fix building on gentoo hosts

This patch fixes the profile autodetect.  If the profile was passed at install
time, it would overridden by the environment.d script.  This was fixed by
accepting the value passed by the user, if one was passed.

The enviroment.d file is run outside of chroot, because of this eselect will
not be available on non-gentoo systems.  We change the behavior to work
elsewhere, it was not working on non-gentoo systems and giving bad results on
gentoo systems (returing values from the host, not the guest being built).

This patch also fixes shm detection by checking if it is mounted already.

Change-Id: Ie58d8e19529a731bfbc9eeb4bb246988d1aaa772

elements/gentoo/bin/install-packages

@@ -58,9 +58,13 @@ function unfix_shm {
 
 function install_gentoo_packages {
     RUN_ONCE_SHM='1'
+    if ! grep -q /dev/shm /proc/mounts; then
         fix_shm
         emerge $@
         unfix_shm
+    else
+        emerge $@
+    fi
 }
 
 TEMP="$(getopt -o huem: -n ${SCRIPTNAME} -- ${@})"

elements/gentoo/environment.d/00-gentoo-distro-name.bash

@@ -1,2 +1,2 @@
 export DISTRO_NAME=gentoo
-export GENTOO_PROFILE=$(eselect profile show | tail -n 1)
+export GENTOO_PROFILE=${GENTOO_PROFILE:-'default/linux/amd64/13.0'}