Implement and use loadPodSpecFromFile which loads and returns PodSpec object
from YAML or JSON file. Use this function in the places where LoadPodFromFile
is used to load Pod object and then return the PodSpec portion of it. This
also removes the dependency on //pkg/volume/util and its dependencies (thus,
making kubeadm more lean).
Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>