Dockerfile: add dockerfile

workaround https://github.com/gentoo/gentoo-docker-images/issues/79

Dockerfile

+FROM gentoo/portage:latest as portage
+FROM gentoo/stage3-amd64-nomultilib:latest
+
+COPY --from=portage /var/db/repos/gentoo /var/db/repos/gentoo
+
+ENV ACCEPT_KEYWORDS="~amd64" \
+    EMERGE_DEFAULT_OPTS="--jobs=4 --quiet" \
+    FEATURES="-ipc-sandbox -network-sandbox -pid-sandbox" \
+    MAKEOPTS="-j4" \
+    USE="-perl"
+
+# https://github.com/gentoo/gentoo-docker-images/issues/79
+RUN emerge --unmerge dev-python/setuptools dev-python/certifi  \
+ && emerge dev-vcs/git app-portage/repoman dev-util/pkgcheck