Raise some timeouts to 180s, in test code.

Raise some timeouts to 180s, in test code.

Slow runs of buildfarm members chipmunk, hornet and mandrill saw the
shorter timeouts expire.  The 180s timeout in poll_query_until has been
trouble-free since 2a0f89cd717ce6d49cdc47850577823682167e87 introduced
it two years ago, so use 180s more widely.  Back-patch to 9.6, where the
first of these timeouts was introduced.

Reviewed by Michael Paquier.

Discussion: https://postgr.es/m/20181209001601.GC2973271@rfd.leadboat.com