consensus: fix expected condition variable exception

[andrwng]

The Seastar docs[1] say wait() returns condition_variable_timed_out, not
timed_out_error. This resulted in error logs like:

INFO  2022-07-29 00:03:16,777 [shard 0] raft - [group_id:5, {kafka/topic-fhmhqjvhxd/4}] consensus.cc:2757 - Starting leadership transfer from {id: {5}, revision: {32}} to {id: {4}, revision: {32}} in term 1
INFO  2022-07-29 00:03:16,777 [shard 0] raft - [group_id:5, {kafka/topic-fhmhqjvhxd/4}] consensus.cc:2660 - transfer leadership: waiting for node {id: {4}, revision: {32}} to catch up
...
ERROR 2022-07-29 00:03:26,777 [shard 0] rpc - Service handler threw an exception: seastar::condition_variable_timed_out (Condition variable timed out)
// ... no corresponding message about the end of the leadership transfer

[1] https://docs.seastar.io/master/classseastar_1_1condition__variable.html#a69703300a8e56a520269062f062aebda

Partially fixes #5378
I think this also fixes #5461

[andrwng]

I took a quick look around the codebase for other usages of ss:timed_out_error and looks like our usage is correct elsewhere (usually accompanied by with_timeout() rather than a condition variable)

[piyushredpanda]

Awesome find, @andrwng!

[ajfabbri]

Nice work. +1 (pending CI)

[andrwng]

/backport v22.1.x

[andrwng]

/backport v21.11.x

[dotnwat]

excellent find!