fixes and improvements

[dpavle]

Description

1. Removed python-pexpect package from the apt install task in packages.yml
2. Become unprivileged user with sudo in configure command instead of within Ansible

Motivation and Context

1. python-pexpect doesn't exist in Ubuntu 22.04 (under that name), and it's handled by pip a step below anyway, so there's no reason to install it here.
2. Ansible doesn't recommend becoming an unprivileged user, and since we're using the command module, it is safer to just use sudo -u to do this.

How Has This Been Tested?

Installed, reconfigured and uninstalled vsts-agent on a Ubuntu 22.04 virtual machine using the role

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)