[baremetal] Use upstream lab proxy for keyservers

[baremetal] Use upstream lab proxy for keyservers

Proxy chainloading does not always work for keyserver requests, so:
- mv common.infra.lab_proxy_pdf common.include.lab_proxy_pdf;
- mv common.include.proxy common.include.maas_proxy;
- include lab_proxy_pdf after each maas_proxy, so if upstream_proxy
  is defined, it will override the MaaS proxy;

JIRA: FUEL-317

Change-Id: I63749be0d350ea73ea2cf6e629710766b14ecb73
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>