net.box: fix fetching of schema of an old version

After 2.2.0-633-gaa0964ae1 ('net.box: fix schema fetching from 1.10/2.1
servers') net.box expects that _vcollation system view exists on a
tarantool server of 2.2.1+ version. This is however not always so: a
server may be run on a new version of tarantool, but work on a schema of
an old version.

The situation with non last schema is usual for replication cluster in
process of upgrading: all instances run on the new version of tarantool
first (no auto-upgrade is performed by tarantools in a cluster). Then
box.schema.upgrade() should be called, but the instances should be
operable even before the call.

Before the commit net.box was unable to connect a server if it is run on
a schema without _vcollation system view (say, 2.1.3), but the server
executable is of 2.2.1 version or newer.

Note: I trim tests from the commit to polish them a bit more, but
include the fix itself to 2.4.1 release.

Follows up #4307
Fixes #4691