Summary:
With this diff -
1. We install setuptools/wheel inside YNP virtual venv.
2. Clean the node-agent directory on the DB node during purging.
3. Minor fixes in backup_utils installation script.
4. Installs backup utils for onprem nodes as well.
5. Ensure that `XDG_RUNTIME_DIR` is not exported if it is already present.

Test Plan:
itest pipeline.
test suite with regex: ynp, custom_ybdb_os_qualification, patching
https://jenkins.dev.yugabyte.com/blue/organizations/jenkins/dev-itest-job/detail/dev-itest-job/29381/pipeline

Reviewers: nsingh, anijhawan

Reviewed By: nsingh, anijhawan

Differential Revision: https://phorge.dev.yugabyte.com/D42478