Return error from createContainerURL if storage settings are not configured

[peterbom]

This fixes a CI built timeout caused by the aks-periscope pods crash-looping.

The crashing behaviour was introduced by #96 but only occurs intermittently because the the pods are briefly in Ready state, so the kubectl -n aks-periscope wait po --all --for condition=ready --timeout=240s command sometimes completes successfully.

Previously to the above change, the createContainerURL function used to fail with an error due to no kubeconfig file existing, meaning that the process would complete (and sleep) without attempting to write anything to blob storage. Following that change, the absence of storage configuration would fail without returning an error, and the process would attempt to write to an empty blob URL, resulting in a panic and crash.

This fixes that function so it explicitly returns an error if storage settings are not configured, which seems like it should be the desired behaviour anyway.

[codecov-commenter]

Codecov Report

Merging #156 (a895f15) into master (48270ee) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #156   +/-   ##
=======================================
  Coverage   68.98%   68.98%           
=======================================
  Files          11       11           
  Lines         345      345           
=======================================
  Hits          238      238           
  Misses         85       85           
  Partials       22       22           

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[Tatsinnit]

☕️🎉