Changes to support refactor in frappe pg-poc branch (#15287)

* Remove quotes from sql to make it compatible with postgres as well

* Fix queries
- Replace mysql specifc queries with standard ones

* Make repo URL chages to test pg-poc

* Add root passowrd to test site config

* Fix quotes issue

* Remove debug flag from a pricing rule query

* Remove python 3.6 version from travis.yml

* Fix improper query issue

* Fix incorrect query

* Fix a query

- This fix need to be changed when we will  start supporting postgres
since date_format is not supported by postgres

* Get price list map as dict

* Convert price_list_currency_map to dict

test_sites/test_site/site_config.json

@@ -7,6 +7,7 @@
  "mail_password": "test",
  "admin_password": "admin",
  "run_selenium_tests": 1,
+ "root_password": "travis",
  "host_name": "http://localhost:8000",
  "install_apps": ["erpnext"]
 }