handle outdated version of eksctl

[dima-naboka]

Goal

Avoid the situation when an outdated version of eksctl prevents starting a newer (unsupported by ekstl) version of K8s e.g. eksctl 0.20.0 and EKS 1.20 (ticket #25221)

[2021-08-17 19:46:08,793] [25987/MainThread] [INFO] [root] 2021-08-17T19:46:08Z [ℹ]  eksctl version 0.20.0
..
[2021-08-17 19:46:08,793] [25987/MainThread] [INFO] [root] Error: invalid version, supported values: 1.13, 1.14, 1.15, 1.16

Notes

current logic in def get_eksctl_or_fetch() present several issues:

1. check for outdated version of eksctl in DATA_DIR/tmp/local_eksctl/ or system-wide with which eksctl
2. when plugin does download eksctl, looks like untar should be executed for eksctl_$(uname -s)_amd64.tar.gz not eksctl.tar.gz

[dima-naboka]

adding ticket 26641