tests: Update world before emerging packages

To fix issues with out of date stage3/Docker image

tests/resources/emerge-ebuild.sh

@@ -22,6 +22,14 @@ fi
 export FEATURES="binpkg-multi-instance -news -ipc-sandbox -network-sandbox -pid-sandbox"
 export PORTAGE_RSYNC_EXTRA_OPTS="-q"
 
+# Show emerge info for troubleshooting purposes
+emerge --info
+
+# Update @world, to fix issues with out of date gentoo/stage3-amd64 images
+# Workaround for bug https://bugs.gentoo.org/723352
+emerge --quiet-build --buildpkg --usepkg sys-libs/libcap
+emerge --quiet-build --buildpkg --usepkg --update --changed-use --deep --with-bdeps=y @world
+
 EBUILD_PATHS=("${@}")
 
 # Emerge the ebuilds in a clean stage3