Rework pull-tester scripts, disable blockchain tester

Re-organize the pull-tester scripts a bit.

And disables running the blockchain tester, it is not working properly
on the pull-tester machine for reasons I cannot explain (fails to start).
Disable code-coverage builds for now

Not working on the pull-tester machine, 'make cov' hangs there.
Merge pull request #3078 from gavinandresen/pulltester

Rework pull-tester scripts, disable blockchain tester