Remove hard-coded postgres name/port

[igor-sirotin]

Problem

Tests seems to be failing to run in parallel in CI:

docker: Error response from daemon: Conflict. The container name "/status-go-test-db" is already in use by container "2723e6e32c65e7a5130fe5ad94d63f3697608879a860dff2f714b71294fcc6dd". You have to remove (or rename) that container to be able to reuse that name.

Implementation

Parametrize:

1. docker container name
   

   status-go/_assets/ci/Jenkinsfile.tests

   Line 28 in ea6107b

   DB_CONT = 'status-go-test-db'

2. postgres port
   

   status-go/postgres/helpers.go

   Lines 10 to 11 in ea6107b

   	DefaultTestURI = "postgres://postgres@127.0.0.1:5432/postgres?sslmode=disable"
   	DropTableURI = "postgres://postgres@127.0.0.1:5432/template1?sslmode=disable"

[igor-sirotin]

cc @jakubgs