Tests for CPP Code generation and some Python3 improvements (#961)

* Basic pytest configuration

* Added unit_test script that triggers pytest

* Changed "fixtures" to fixture_path

This is consistent with pytest's tmp_path

* Initial unit tests for esphome.helpers

* Disabled coverage reporting for esphome/components.

Focus initial unittest efforts on the core code.

* Migrated some ip_address to hypothesis

* Added a hypothesis MAC address strategy

* Initial tests for core

* Added hypothesis to requirements

* Added tests for core classes

TestTimePeriod
Lambda
ID
DocumentLocation
DocumentRange
Define
Library

* Updated test config so package root is discovered

* Setup fixtures and inital tests for pins

* Added tests for validate GPIO

* Added tests for pin type

* Added initial config_validation tests

* Added more tests for config_validation

* Added comparison unit tests

* Added repr to core.TimePeriod. Simplified identifying faults in tests

* Fixed inverted gt/lt tests

* Some tests for Espcore

* Updated syntax for Python3

* Removed usage of kwarg that isn't required

* Started writing test cases

* Started writing test cases for cpp_generator

* Additional docs and more Python3 releated improvements

* More test cases for cpp_generator.

* Fixed linter errors

* Add codegen tests to ensure file API remains stable

* Add test cases for cpp_helpers

requirements_test.txt

@@ -21,4 +21,5 @@ pexpect
 pytest==5.3.2
 pytest-cov==2.8.1
 pytest-mock==1.13.0
+asyncmock==0.4.2
 hypothesis==4.57.0