MQE-1676: Static check for unused arguments in action group.

[soumyau]

Description

Scans action group files and finds unused arguments.

1. For merging action groups, checks unused arguments for the every action group xml string to avoid arguments getting flagged for removal of steps.
2. For extending action groups, checks unused arguments for parent and child action group xml strings.
   Arguments of child action group that are also defined in it's parent but are used only in parent are not reported as unused.

Fixed Issues (if relevant)

1. magento/magento2-functional-testing-framework#<issue_number>: Issue title
2. ...

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/verification tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)
• Changes to Framework doesn't have backward incompatible changes for tests or have related Pull Request with fixes to tests

[coveralls]

Coverage decreased (-0.06%) to 51.919% when pulling 1c7c6ce on MQE-1676 into c069eca on develop.

[soumyau]

Addressed all review comments

[jilu1]

In the case of action group merging with removal, the script gives a false result.

File "/Users/jilu/Code/magento5/app/code/Magento/CatalogRule/Test/Mftf/ActionGroup/AssertCatalogRuleInGridActionGroup.xml,/Users/jilu/Code/magento5/ee/app/code/Magento/CatalogRuleStaging/Test/Mftf/ActionGroup/AssertCatalogRuleInGridActionGroup.xml"
contains action group(s) with unused arguments.
		
	 AssertCatalogRuleInGridActionGroup has unused argument(s): status

[jilu1]

Looks good