add imagePullSecrets option to podconfig

[markstubb]

This should allow the end user to use a -podconfig yaml to specify affinity and imagePullSecrets for the scand-agent pod that scand-manager launches.

[markstubb]

example podconfig.yml is

apiVersion: v1
kind: PodSpec
affinity:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchExpressions:
        - key: scandallowed
          operator: In
          values:
          - "true"
imagePullSecrets:
  - name: secret1
  - name: secret2