install: allowing `install` over interrupted previous installation

[nbusseneau]

Bug report

If cilium install is abruptly interrupted while in progress, the rollback code does not have a chance to run and there are leftover resources.

One solution could be to have cilium install be more lenient with existing resources and accepting them as-is or editing them instead of failing when they are already present.

• Detected in #584.
• Related to #149.

How to reproduce the issue

1. Run cilium install
2. Have it abruptly interrupted (e.g. kill process) while in progress
3. Run cilium install again
4. Fails due to partially installed resources (e.g. hubble-server-certs)

[errordeveloper]

Might be a good reason to implement https://github.com/cilium/cilium-cli/issues/115.

[xiaods]

my first install is successful, when i install agagin, it report error sucks