Add more equery options
_gentoo_packages, _portage: Added sets completion

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>
_gentoo_packages, _portage: reworked sets completion, added portage options

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>
_portage: add prepare, configure and test to ebuild completion

partial fix for
X-Gentoo-Bug: 439978
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=439978