Cleanup some problems in new Perl test code

Cleanup some problems in new Perl test code

Noted by Tom Lane:
- PostgresNode had a BEGIN block which created files, contrary to
  perlmod suggestions to do that only on INIT blocks.
- Assign ports randomly rather than starting from 90600.

Noted by Noah Misch:
- Change use of no-longer-set PGPORT environment variable to $node->port
- Don't start a server in pg_controldata test
- PostgresNode was reading the PID file incorrectly; test the right
  thing, and chomp the line we read from the PID file.
- Remove an unused $devnull variable
- Use 'pg_ctl kill' instead of "kill" directly, for Windos portability.
- Make server log names more informative.

Author: Michael Paquier