Openshift action hook can't access environment variables - database

Question

For my application on Openshift, I am trying to write a pre_build script that accesses the database. The goal is to have migration scripts between database versions that are executed when the code is deployed. The script would compare the current database version with the version needed by the application code and then run the correct script to migrate the database.
Now the problem is that apparently the pre_build script is executed on Jenkins and not on the destination cartridge and therefore the environment variables with the database connection arguments are not available.
This is the pre_build script that I've written so far:
#!/usr/bin/env python
print "*** Database migration script ***"
# get goal version
import os
homedir = os.environ["OPENSHIFT_HOMEDIR"]
migration_scripts_dir = homedir + "app-root/runtime/repo/.openshift/action_hooks/migration-scripts/"
f = open(migration_scripts_dir + "db-version.txt")
goal = int(f.read())
f.close()
print "I need database version " + str(goal)
# get database connection details
# TODO: find a solution of not hard coding the connection details here!!!
# Maybe by using jenkins environment variables like OPENSHIFT_APP_NAME and JOB_NAME
db_host = "..."
db_port = "..."
db_user = "..."
db_password = "..."
db_name = "..."
import psycopg2
try:
conn = psycopg2.connect("dbname='" + db_name + "' user='" + db_user + "' host='" + db_host + "' password='" + db_password + "' port='" + db_port + "'")
print "Successfully connected to the database"
except:
print "I am unable to connect to the database"
cur = conn.cursor()
def get_current_version(cur):
try:
cur.execute("""SELECT * from db_version""")
except:
conn.set_isolation_level(0)
cur.execute("""CREATE TABLE db_version (db_version bigint NOT NULL)""")
cur.execute("""INSERT INTO db_version VALUES (0)""")
cur.execute("""SELECT * from db_version""")
current_version = cur.fetchone()[0]
print "The current database version is " + str(current_version)
return current_version
def recursive_execute_migration(cursor):
current_version = get_current_version(cursor)
if (current_version == goal):
print "Database is on the correct version"
return
elif (current_version < goal):
sql_filename = "upgrade" + str(current_version) + "-" + str(current_version + 1) + ".sql"
print "Upgrading database with " + sql_filename
cursor.execute(open(migration_scripts_dir + sql_filename, "r").read())
recursive_execute_migration(cursor)
else:
sql_filename = "downgrade" + str(current_version) + "-" + str(current_version - 1) + ".sql"
print "Downgrading database with " + sql_filename
cursor.execute(open(migration_scripts_dir + sql_filename, "r").read())
recursive_execute_migration(cursor)
conn.set_isolation_level(0)
recursive_execute_migration(cur)
cur.close()
conn.close()
Is there another way of doing automatic database migrations?
Thanks for your help.