997970: For v1 certs, skip unknown content types

Add 'kickstart' to the known content types OID map.

If an unknown content type is found while generating
cert v1 extentions, skip it. Previously it would
try to use 'null' as the content type and fail.
Merge pull request #346 from candlepin/alikins/997970_kickstart_content_type

997970: For v1 certs, skip unknown content types