Use Azure STORAGE_ACCOUNT_NAME env if set during init-vhd

Update docs

Author: kkeshavamurthy

docs/book/src/capi/providers/azure.md

@@ -7,6 +7,7 @@ These images are designed for use with [Cluster API Provider Azure]([Cluster API
 - An Azure account
 - The Azure CLI installed and configured
 - Set environment variables for `AZURE_SUBSCRIPTION_ID`, `AZURE_CLIENT_ID`, `AZURE_CLIENT_SECRET`
+- Set optional environment variables `RESOURCE_GROUP_NAME`, `STORAGE_ACCOUNT_NAME` & `AZURE_LOCATION` to override the default values
 
 ## Building Images
 

images/capi/packer/azure/scripts/init-vhd.sh

@@ -5,8 +5,8 @@
 echo "Sign into Azure"
 tracestate="$(shopt -po xtrace)"
 set +o xtrace
-az login --service-principal -u ${AZURE_CLIENT_ID} -p ${AZURE_CLIENT_SECRET} --tenant ${AZURE_TENANT_ID} >/dev/null 2>&1 
-az account set -s ${AZURE_SUBSCRIPTION_ID} >/dev/null 2>&1 
+az login --service-principal -u ${AZURE_CLIENT_ID} -p ${AZURE_CLIENT_SECRET} --tenant ${AZURE_TENANT_ID} >/dev/null 2>&1
+az account set -s ${AZURE_SUBSCRIPTION_ID} >/dev/null 2>&1
 eval "$tracestate"
 
 echo "Create storage account"
@@ -15,7 +15,7 @@ export AZURE_LOCATION="${AZURE_LOCATION:-southcentralus}"
 az group create -n ${RESOURCE_GROUP_NAME} -l ${AZURE_LOCATION} --tags ${TAGS:-}
 CREATE_TIME="$(date +%s)"
 RANDOM_SUFFIX="$(head /dev/urandom | LC_ALL=C tr -dc a-z | head -c 4 ; echo '')"
-export STORAGE_ACCOUNT_NAME="capi${CREATE_TIME}${RANDOM_SUFFIX}"
+export STORAGE_ACCOUNT_NAME="${STORAGE_ACCOUNT_NAME:-capi${CREATE_TIME}${RANDOM_SUFFIX}}"
 az storage account check-name --name ${STORAGE_ACCOUNT_NAME}
 az storage account create -n ${STORAGE_ACCOUNT_NAME} -g ${RESOURCE_GROUP_NAME}