Avoid using subprocess to call psql

[frafra]

psycopg2 is imported. It would be better to rely on it instead of requiring to install psql as additional dependency, in my opinion.

docker-osm/docker-imposm/importer.py

Line 271 in f345249

call(command)

[NyakudyaA]

I think running SQL scripts using psycopg2 has some drawbacks i.e https://stackoverflow.com/questions/17261061/execute-sql-schema-in-psycopg2-in-python