Added a utility to help with validating structs. This utility accepts
validators and runs them. If any of the validators fail, then the
error is wrapped with a given base message and returned.
Added validators for checking different attributes of a task
definition.
Added test code to test task validators.
Retrofitted scheduler.go to just log the task validation error and
terminate. If task validation does not report any error, then the
tasks are provided to the scheduler and elektron registers itself
with Mesos.
