Align legacy EC2 context variables across one-apps, documentation, and tests

[OpenNebulaSupport]

Description

Some legacy EC2-related context variables are no longer documented in the current OpenNebula context attribute reference, but at least some of them are still consumed by the guest-side contextualization code in one-apps.

This was noticed after a customer reported that EC2_HOSTNAME, which is documented in older OpenNebula versions such as 5.12, is not listed in the 6.10 documentation. However, when tested on OpenNebula 6.10.5, setting EC2_HOSTNAME in the VM CONTEXT section still takes effect inside the guest.

After checking internally, these variables do not appear to be handled by one-ee / core in 6.10 or 7.2. The behavior seems to come from one-apps / guest contextualization scripts.

Legacy variables to review

The following variables were documented in older versions but are missing from the 6.10 / 7.2 context attribute documentation:

• EC2_HOSTNAME
• EC2_PUBLIC_KEY
• GATEWAY_IFACE
• ETHx_ALIASy_EXTERNAL

Notes:

• EC2_HOSTNAME and EC2_PUBLIC_KEY appear to still be present in one-apps.
• EC2_HOSTNAME was confirmed to work on OpenNebula 6.10.5.
• ETHx_IPV6 and ETHx_ALIASy_IPV6 are not included here because they are already documented as legacy aliases for ETHx_IP6 and ETHx_ALIASy_IP6.

Expected outcome

Align the behavior and public reference across:

• one-apps contextualization code
• OpenNebula documentation
• Development/testing coverage

The issue should clarify whether these legacy variables should be:

1. kept and documented as supported/legacy variables for backward compatibility,
2. explicitly deprecated but still accepted by contextualization scripts,
3. or removed/cleaned up if they are only leftovers from the discontinued Cloud-Bursting/EC2 workflow.