reference: Replace EnsureTagged with TagNameOnly
reference: Replace EnsureTagged with TagNameOnly

The common use case for this function is to add a default tag if the
reference only has a name. The current behavior only adds the default
tag if there is no *tag*, which requires most callers to check for a
digest. Change the behavior to only add default tags to name-only
references, and change the name to reflect this. The documentation
already described the new behavior, so it does not need to be changed.

Signed-off-by: Aaron Lehmann <8ecfc6017a87905413dcd7d63696a2a4c351b604@docker.com>

konstruktoid/distribution,mikebrow/distribution,shyr/distribution,cezarsa/distribution,huamai-io/distribution,mikebrow/distribution,spacexnice/distribution,estesp/distribution,dmcgowan/distribution,dmcgowan/distribution,yuwaMSFT2/distribution,duglin/distribution,docker/distribution,miminar/distribution,sadlil/distribution,jwhonce/distribution,konnase/distribution,huamai-io/distribution,jwhonce/distribution,estesp/distribution,harrisonfeng/distribution,manoj535/distribution,shyr/distribution,harrisonfeng/distribution,cezarsa/distribution,manoj535/distribution,miminar/distribution,jzwlqx/distribution,sergeyfd/distribution,konnase/distribution,thaJeztah/distribution,docker/distribution,sadlil/distribution,vdemeester/distribution,duglin/distribution,konstruktoid/distribution,thaJeztah/distribution,vdemeester/distribution,yuwaMSFT2/distribution,sergeyfd/distribution,spacexnice/distribution,jzwlqx/distribution