Better error handling to avoid exporter crash

[jneo8]

Relate to:

• hardware-exporter crashes after connecting to redfish on Dell PowerEdge R740 hardware-observer-operator#109
• hardware-exporter crashes after connecting to redfish on Huawei 2288H V5 hardware-observer-operator#108
• storage endpoint should be storages instead of storage hardware-observer-operator#91

I purpose to add an error handling to BlockingCollector class and provide a a default failing metrics to notice people that the specific collector is failing.