Dockefile.minimal: revamp
Dockefile.minimal: revamp

This commit basically does two things:

1. Update alpine to 3.6 and golang to 1.9.5. This, among the other
things, makes it possible to build cfssl on non-x86 architectures
(as the newer dockerhub images are now multiarch).

2. Minimize image size even more by using docker multi-stage build.
This simplifies the build a bit (no need to remove anything), and
makes the resulting image leaner (the size is reduced from ~90 to
~50 MB on ppc and x86_64).

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

geligaoli/cfssl,geligaoli/cfssl,cloudflare/cfssl,geligaoli/cfssl,cloudflare/cfssl,drcapulet/cfssl,drcapulet/cfssl,cloudflare/cfssl,drcapulet/cfssl,geligaoli/cfssl,cloudflare/cfssl,geligaoli/cfssl,drcapulet/cfssl,drcapulet/cfssl