Use a longer connection timeout in pg_isready test.

Use a longer connection timeout in pg_isready test.

Buildfarm members skink and sungazer have both recently failed this
test, with symptoms indicating that the default 3-second timeout
isn't quite enough for those very slow systems.  There's no reason
to be miserly with this timeout, so boost it to 60 seconds.

Back-patch to all versions containing this test.  That may be overkill,
because the failure has only been observed in the v10 branch, but
I don't feel like having to revisit this later.