test-release.sh: Move test-suite setup to beginning of the script

Summary:
We want to catch failures early before do the full 3 stage build.

The goal here is to avoid running through the whole build process and have
it fail at the end (and not create the binary packages), just because
some prerequisites failed to install.

Reviewers: rovka, hans

Reviewed By: hans

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D36422

llvm-svn: 310939