(PDB-2982) Clarify args of embeddable-certname.
(PDB-2982) Clarify args of embeddable-certname.

Clarify that `puppetdb.queue/embeddable-certname` and the two
functions it calls to determine the certname length all take the
metadata command name, rather than the command name that the rest of
PuppetDB uses.

senior/puppetdb,rbrw/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,mullr/puppetdb,mullr/puppetdb,rbrw/puppetdb,mullr/puppetdb,waynr/puppetdb,rbrw/puppetdb,rbrw/puppetdb,waynr/puppetdb,senior/puppetdb,puppetlabs/puppetdb,senior/puppetdb,waynr/puppetdb,puppetlabs/puppetdb,mullr/puppetdb,rbrw/puppetdb,mullr/puppetdb,senior/puppetdb,puppetlabs/puppetdb,waynr/puppetdb