TravisCI and AppVeyor run the tests in very slow VMs.
Some of our tests can't cope with that. Running less tests
in parallel should make them somewhat less flakey.

(cherry picked from commit b0a6b979)

(cherry picked from commit 8c23f20c)

The new build script, ci.go, replaces some of the older shell scripts.
ci.go can compile go-ethereum, run the tests, create release archives
and debian source packages.

(cherry picked from commit 6c33ba14)