Improve translatability of some getObjectDescription() messages.

Improve translatability of some getObjectDescription() messages.

Refactor some cases in getObjectDescription so that the translator has
more control over phrase order in the translated messages.  This doesn't
cause any changes in the English results.  (I was sorely tempted to
reorder "... belonging to role %s in schema %s" into "... in schema %s
belonging to role %s", but refrained.)

In principle we could back-patch this, but since translators have not
complained about these cases previously, it seems better not to thrash
the translatable strings in back branches.

Kyotaro Horiguchi, tweaked a bit by me

Discussion: https://postgr.es/m/20180522.182020.114074746.horiguchi.kyotaro@lab.ntt.co.jp