kubernetes: improve error message if pod create fails
kubernetes: improve error message if pod create fails

Updates golang/go#14112

Change-Id: I53e42647e5a8b22cfb70b78fc4571ff78dd23289
Reviewed-on: https://go-review.googlesource.com/18984
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,proppy/build,proppy/build,golang/build,proppy/build,golang/build,proppy/build