Split out configuration validation into helper class

Validation of the configuration started making the `Configuration` class
a bit long. Separate out the concern into a separate helper class.

Change-Id: I267addc42240d235a23e03ff69be71a396a27613
Reviewed-on: http://gerrit.causes.com/40382
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>