Refactor and fix TAP tests of pg_rewind

Refactor and fix TAP tests of pg_rewind

* Don't pass arguments to prove, since that's not supported on perl 5.8
which is the minimum version supported by the TAP tests. Refactor the
test files themselves to run the tests twice, in both local and remote mode.

* Use eq rather than == for string comparison. This thinko caused the remote
versions of the tests to never run.

* Add "use strict" and "use warnings", and fix warnings that that produced.

* Increase the delay after standby promotion, to make the tests more robust.

* In remote mode, the connection string to the promoted standby was
incorrect, leading to connection errors.

Patch by Michael Paquier, to address Peter Eisentraut's report.