Reassemble postgresql parameters when major version became known (#395)

* Reassemble postgresql parameters when major version became known

Otherwise we were writing some "unknown" parameters into postgresql.conf
and postgres was refusing to start. Only 9.3 was affected.

In addition to that move rename of wal_level from hot_standby to replica
into get_server_parameters method. Now this rename is handled in a
single place.

* Bump etcd and consul versions

.travis.yml

@@ -5,7 +5,7 @@ python:
 - "3.4"  # 2.7 and 3.5 are preinstalled by default
 env:
   global:
-  - ETCDVERSION=3.0.15 ZKVERSION=3.4.9 CONSULVERSION=0.7.2
+  - ETCDVERSION=3.0.17 ZKVERSION=3.4.9 CONSULVERSION=0.7.4
   - PYVERSIONS="2.7 3.4 3.5"
   matrix:
   - TEST_SUITE="python setup.py"