Split PXE fixture into multiple components

Split up setup_pxe_provision fixture into
* setup_pxe_server()
* setup_pxe_menu()
* setup_pxe_image()
* setup_pxe_customization_template()
Added Host Add page and test

Hosts page class
* Added _configuration_button_locator, _add_new_host_locator, _remove_host_locator to Hosts class
* Added @add_button property, @remove_button property to Hosts class
* Added click_add_new_host() method to Hosts class
* Added does_host_exist() method to Hosts class
* Added check_host_and_refresh() method to Hosts class
* Added click_remove_host() method to Hosts class

Add subpage
* Added new Add page for Hosts subpages

test_infrastructure_provider_pages.py
* Added new test test_host_add() to test_infrastructure_provider_pages.py
* Added new test test_host_delete() to test_infrastructure_provider_pages.py
* Added new single_host_data fixture to test_infrastructure_provider_pages.py

Page base class
* Added _wait_for_invisible_element to Page class

Template data
* Added template data
Added new IPMI backend for both host power control and verification

Added utils/ipmi.py
* is_power_on() method for determining chassis power
* power_on() method for turning on power
* power_off() method for turning off power
* power_reset() method for hard reset of power state, respects current power state and deals accordingly
Merge pull request #229 from psav/ipmi_backend

Added new IPMI backend for both host power control and verification