[6.15.z] Refactor ipv6 http_proxy code

[Satellite-QE]

Cherrypick of PR: #16928

Problem Statement

• The current design of enable_ipv6_http_proxy and disable_ipv6_http_proxy is incorrect and confusing.
• Satellite and Capsule classes of robottelo/hosts.py have enable_ipv6_http_proxy. The one present in Satellite is for setting HTTP proxy in Satellite settings(content and general HTTP proxy). And the one in Capsule is for enabling HTTP proxy for dnf and rhsm.
• This design doesn't allow Satellite to set dnf and rhsm proxies.

Solution

• Removeenable_ipv6_http_proxy and disable_ipv6_http_proxy from Satellite and Capsule classes.
• Add enable_satellite_http_proxy and disable_satellite_http_proxy to enable/disable ipv4/ipv6 HTTP proxy.
• Add enable_satellite_ipv6_http_proxy in Satellite class to set Ipv6 HTTP proxy in Satellite settings, rhsm, and dnf.
• Add enable_ipv6_dnf_and_rhsm_proxy to ContenHost class so all the three kind of hosts can use it (Satellite, Capsule, Client).
• This PR also removes test_installer_modules_check and covers it in test_satellite_installation.
• It also remove http_proxy test parameterization for test_capsule_installation as it'll be covered by default (Satellite will have HTTP proxy enabled)

Related Issues

• SAT-29467
• Depends on satellite-jenkins#1556