We had '_get_microversion_for_list' and '_get_microversion_for', the
latter of which simply called the former. There's no reason for this
distinction and I suspect it's simply there because of legacy reasons.
Merge them.
Change-Id: I5124fa0005e809891a1fc970c6ccdc5f4a766d33
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>