Simplify the passing of KUBECONFIG

According to `man podman run` if we simply pass `-e KUBECONFIG` to
the podman invocation: "If an environment variable is spec‐
ified without a value, Podman checks the host environment for a value
and set the variable only if it is set on the host"

So let's just do that and drop the current more complex fragile logic.

Tested with:

* No KUBECONFIG set
unset KUBECONFIG; ./pattern.sh make install
make -f common/Makefile operator-deploy
make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/multicloud-gitops'
Checking prerequisites:
  Check for 'git helm oc ansible': OK
  Check for python-kubernetes: OK
  Check for kubernetes.core collection: OK
Checking repository:
  https://github.com/mbaldessari/multicloud-gitops.git - branch script-fix: Running inside a container: Skipping git ssh checks
Running helm:
Error: Kubernetes cluster unreachable: Get "https://localhos:6443/version"

* With KUBECONFIG set
export KUBECONFIG=~/sno1-kubeconfig
./pattern.sh make install
make -f common/Makefile operator-deploy
make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/multicloud-gitops'
Checking prerequisites:
  Check for 'git helm oc ansible': OK
  Check for python-kubernetes: OK
  Check for kubernetes.core collection: OK
Checking repository:
  https://github.com/mbaldessari/multicloud-gitops.git - branch script-fix: Running inside a container: Skipping git ssh checks
Running helm:
WARNING: Kubernetes configuration file is group-readable. This is insecure. Location: /home/michele/sno1-kubeconfig
Release "multicloud-gitops" does not exist. Installing it now.
NAME: multicloud-gitops
LAST DEPLOYED: Mon Sep  4 07:04:16 2023
NAMESPACE: default
STATUS: deployed
REVISION: 1
TEST SUITE: None
make[1]: Leaving directory '/home/michele/Engineering/cloud-patterns/multicloud-gitops'
make load-secrets
make[1]: Entering directory '/home/michele/Engineering/cloud-patterns/multicloud-gitops'
make -f common/Makefile load-secrets
...

Author: mbaldessari

scripts/pattern-util.sh

@@ -25,19 +25,12 @@ fi
 # $HOME is mounted as itself for any files that are referenced with absolute paths
 # $HOME is mounted to /root because the UID in the container is 0 and that's where SSH looks for credentials
 
-# We must pass -e KUBECONFIG *only* if it is set, otherwise we end up passing
-# KUBECONFIG="" which then will confuse ansible
-KUBECONF_ENV=""
-if [ -n "$KUBECONFIG" ]; then
-	KUBECONF_ENV="-e KUBECONFIG=${KUBECONFIG}"
-fi
-
 # Do not quote the ${KUBECONF_ENV} below, otherwise we will pass '' to podman
 # which will be confused
 podman run -it --rm \
 	--security-opt label=disable \
 	-e EXTRA_HELM_OPTS \
-	${KUBECONF_ENV} \
+	-e KUBECONFIG \
 	-v "${HOME}":"${HOME}" \
 	-v "${HOME}":/pattern-home \
 	-v "${HOME}":/root \