In cross model relation contexts, the unit name on the consuming
side of the relation is obfuscated by Juju. Explicitly set the
name of the unit on the relation so providing service can use
this as the key when returning a specific unit's cert and key
for TLS encryption.
Change-Id: Iae93521bc4a3d899560ac304e7b98bfd1d282709
7686150bef