make postgresql collector work with postgres 9.2 or greater

- in pg_stat_activity
- current_query -> query
- procpid -> pid

Defaults to 9.2 or greater syntax but can be configured to work with
older postgresql versions.
default to postgres 9.2
memory_docker: remove py27ism
Merge pull request #598 from sanga/mem_docker_fix

memory_docker: remove py27ism
Merge pull request #597 from sanga/postgres_collector_update

Postgres collector update