[Platform] Install s3cmd on YW yugabyte#5593

Summary: Encrypted backup/restore flow requires s3cmd to be available on YW machine for S3 backups. Still need a solution for azcopy and gsutil as they can't be installed by pip.

Test Plan:
Delete local s3cmd (i.e. run brew uninstall s3cmd) -> run install_python_requirements -> try to backup encrypted at rest universe. Also tested this on a k8s YW leftover from itest run by running
```
pip install s3cmd
```
and rerunning backup on encrypted at rest universe and making sure it works.

Reviewers: sanketh, arnav, wesley, bogdan

Reviewed By: bogdan

Differential Revision: https://phabricator.dev.yugabyte.com/D9315

Author: Daniel Isen

managed/devops/bin/yb_backup.py

@@ -397,7 +397,8 @@ def storage_type():
     def _command_list_prefix(self):
         # If 's3cmd get' fails it creates zero-length file, '--force' is needed to
         # override this empty file on the next retry-step.
-        return ['s3cmd', '--force', '--config=%s' % self.options.cloud_cfg_file_path]
+        return ['s3cmd', '--force', '--no-check-certificate', '--config=%s'
+                % self.options.cloud_cfg_file_path]
 
     def upload_file_cmd(self, src, dest):
         cmd_list = ["put", src, dest]

managed/devops/python_requirements.txt

@@ -45,6 +45,7 @@ pycrypto
 python-dateutil==2.5.3
 python-dotenv==0.6.4
 PyYAML==3.13
+s3cmd==2.0.2
 setuptools>=11.333
 six==1.10.0
 slackclient

managed/devops/python_requirements_frozen.txt

@@ -75,6 +75,7 @@ s3transfer==0.1.13
 six==1.10.0
 slackclient==1.3.2
 stormssh==0.7.0
+s3cmd==2.0.2
 termcolor==1.1.0
 texttable==1.6.2
 typing==3.7.4.3