[cloud] Convert s3 module to use boto3 (#21529)

* replace boto with boto3 for the s3 module

make s3 pep8 and remove from legacy files

fix s3 unit tests

* fix indentation

* s3 module - if we can't create an MD5 sum return None and always upload file

* remove Location.DEFAULT which isn't used in boto3 and tidy up the docs

* pep8

* s3: remove default: null, empty aliases, and required: false from documentation

fix incorrectly documented defaults

* Porting s3 to boto3. Simplify some logic and remove unused imports

* Fix s3 module variables

* Fix a typo in s3 module and remove from pep8 legacy files

* s3: add pagination for listing objects.

Fix logic and use head_object instead of get_object for efficiency.

Fix typo in unit test.

* Fix pagination to maintain backwards compatibility.

Fix incorrect conditional.

Remove redundant variable assignment.

Fix s3 list_object pagination to return all pages

* Use the revised List Objects API as recommended.

* Wrap call to paginated_list in a try/except

Also remembered to allow marker/prefix/max_keys to modify what keys are listed

* Simplify argument

test/runner/requirements/units.txt

@@ -1,4 +1,3 @@
-boto
 boto3
 placebo
 cryptography