Fix username in pg_hba.conf in test script

The script contains a reference to user "heikki", something quite
restrictive. This is changed to "all", which is fine as this is
only a sanity test.

Patch by Samrat Revagade
Make README a bit less confusing

This takes care of correcting some typos, as well as some expressions
that were a bit confusing.

Patch from Samrat Revagade, with some small changes by me.
Remove data directories before node init in test script

Because of the deletion of the new and old data directory was forgotten,
it was simply not possible to run twice in a row the same test.