Rework option set of vacuumlo

Like oid2name, vacuumlo has been lacking consistency with other
utilities for its options:
- Connection options gain long aliases.
- Document environment variables which could be used: PGHOST, PGPORT and
PGUSER.

Documentation and code is reordered to be more consistent. A basic set
of TAP tests has been added while on it.

Author: Tatsuro Yamada
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/c7e7f25c-1747-cd0f-9335-390bc97b2db5@lab.ntt.co.jp

contrib/vacuumlo/t/001_basic.pl

@@ -0,0 +1,9 @@
+use strict;
+use warnings;
+
+use TestLib;
+use Test::More tests => 8;
+
+program_help_ok('vacuumlo');
+program_version_ok('vacuumlo');
+program_options_handling_ok('vacuumlo');