dev-lang/clojure: >=1.9.0 fix sandbox violations

dev-lang/clojure: >=1.9.0 fix sandbox violations

This commit updates the clojure ebuilds to use the latest ebuild
conventions and updates the dependencies to include two new packages.

This is the last in a series of 3 commits that make it possible to build
>=clojure-1.9.0 on gentoo without pulling in any maven dependencies which
trigger network-sandbox violations.

To accomplish this two new packages dev-java/spec-alpha and
dev-java/core-specs-alpha have been added to the tree. They are
dependencies written in clojure that are required to build clojure but
that do not themselves depend on clojure.

Closes: https://bugs.gentoo.org/670680
Closes: https://bugs.gentoo.org/684536
Closes: https://github.com/gentoo/gentoo/pull/14224

Signed-off-by: Tom Gillespie <tgbugs@gmail.com>
Signed-off-by: Kent Fredric <kentnl@gentoo.org>