Update dependency PyYAML to v5.4

[mend-for-github-com]

This PR contains the following updates:

Package	Update	Change
PyYAML (source)	minor	==5.1.2 -> ==5.4

By merging this PR, the below issues will be automatically resolved and closed:

Severity	CVSS Score	CVE	GitHub Issue
High	9.8	CVE-2020-1747	#269
High	9.8	CVE-2019-20477	#270
High	9.8	CVE-2020-14343	#271

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Release Notes

yaml/pyyaml

v5.4

Compare Source

v5.3.1

Compare Source

v5.3

Compare Source

v5.2

Compare Source

• Repair incompatibilities introduced with 5.1. The default Loader was changed,
  but several methods like add_constructor still used the old default
  #​279 -- A more flexible fix for custom tag constructors
  #​287 -- Change default loader for yaml.add_constructor
  #​305 -- Change default loader for add_implicit_resolver, add_path_resolver
• Make FullLoader safer by removing python/object/apply from the default FullLoader
  #​347 -- Move constructor for object/apply to UnsafeConstructor
• Fix bug introduced in 5.1 where quoting went wrong on systems with sys.maxunicode <= 0xffff
  #​276 -- Fix logic for quoting special characters
• Other PRs:
  #​280 -- Update CHANGES for 5.1

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• If you want to rebase/retry this PR, check this box

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[cortx-admin]

Can one of the admins verify this patch?

[ajaysrivas]

This is common package, can't be upgraded without discussion.
Plan is to take up this activity in last sprint of PI-2.