Fix packagecloud_push.sh upload failure for vpp-ext-deps

Fix packagecloud_push.sh upload failure for vpp-ext-deps

- When a new vpp-ext-deps version is created, the
  packagecloud_push.sh script will declare a failure
  for merge jobs if the package already has been
  pushed by another job running in parallel.
  Since vpp-ext-deps will be automatically rebuilt
  by the VPP build, there is no reason to fail the
  merge job if the packagecloud push fails for the
  vpp-ext-deps package.

Signed-off-by: Dave Wallace <[email protected]>
Change-Id: I96edc6948b7f8b654cc66154412e5eb00927266a