Add command defaults to some of the examples

Given the variable name `$PGO_CMD` can involve a lot of context
and given that some of the examples may be run without the
precursor "envs" executable being run, this adds a sane default
of `kubectl` to some of the example scripts, while also indicating
what are acceptable values, should one introspect the scripts.

Issue: #1928

Author: jkatz

examples/create-by-resource/run.sh

@@ -18,6 +18,8 @@
 #########
 
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+# PGO_CMD should either be "kubectl" or "oc" -- defaulting to kubectl
+PGO_CMD=${PGO_CMD:-kubectl}
 
 # A namespace that exists in NAMESPACE env var - see examples/envs.sh
 export NS=pgouser1

examples/custom-config/create.sh

@@ -28,11 +28,8 @@ function echo_info() {
 
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 
-#Error if PGO_CMD not set
-if [[ -z ${PGO_CMD} ]]
-then
-	echo_err "PGO_CMD is not set."
-fi
+# PGO_CMD should either be "kubectl" or "oc" -- defaulting to kubectl
+PGO_CMD=${PGO_CMD:-kubectl}
 
 #Error is PGO_NAMESPACE not set
 if [[ -z ${PGO_NAMESPACE} ]]