add error handling for authentication method.

also, renamed internal field for the ApiClient.
add check for 500 server response code.
use more realistic defaults.

Now 300secs for refresh and 3secs for timeout.
add timer for primary/secondary loading.

Added timers to separately measure the primary versus secondary
load stages.

Also removed unnecessary checking of loading inputs in cache.

Fixes #9
added last.refresh.duration metric.
dropped the array= prefix from the generated array tag.

This prefix is unnecessary and the nodes can be filtered using
server_array.name attribute if needed.
bump to 1.0.0.4 to contain new primary/secondary cache load metrics

Fixes #9