allow yaml files to have yaml extension

[rccrdpccl]

Provisioning with a plan file ending in .yaml instead of .yml results in error, because kcli appends kcli_plan.yml suffix.

kcli create plan -P k8s=true -u https://github.com/rccrdpccl/kcli-manifests/blob/master/k8s-interactive.yaml -P student=testme testme
Trying to retrieve https://github.com/rccrdpccl/kcli-manifests/blob/master/k8s-interactive.yaml/kcli_plan.yml
Retrieving specified plan from https://github.com/rccrdpccl/kcli-manifests/blob/master/k8s-interactive.yaml/kcli_plan.yml to testme
Hit issue with url https://raw.githubusercontent.com/rccrdpccl/kcli-manifests/master/k8s-interactive.yaml/kcli_plan.yml

This PR aims to fix that, and other places where yaml files are only accepted as yml

[karmab]

THANKS for that!