dev: Clearer postgres error messages in postgres-init-dev-db.
dev: Clearer postgres error messages in postgres-init-dev-db.

This uses `pg_isready` to provide a clearer error message if postgres
isn't working.

Fixes #2419.

samatdav/zulip,showell/zulip,rht/zulip,verma-varsha/zulip,andersk/zulip,blaze225/zulip,rishig/zulip,brainwane/zulip,synicalsyntax/zulip,dhcrzf/zulip,eeshangarg/zulip,dawran6/zulip,JPJPJPOPOP/zulip,christi3k/zulip,blaze225/zulip,jrowan/zulip,PhilSk/zulip,sonali0901/zulip,souravbadami/zulip,synicalsyntax/zulip,samatdav/zulip,Galexrt/zulip,vaidap/zulip,jainayush975/zulip,dawran6/zulip,SmartPeople/zulip,kou/zulip,brockwhittaker/zulip,jphilipsen05/zulip,hackerkid/zulip,jrowan/zulip,mahim97/zulip,eeshangarg/zulip,tommyip/zulip,dhcrzf/zulip,vabs22/zulip,andersk/zulip,souravbadami/zulip,jainayush975/zulip,zulip/zulip,mahim97/zulip,zulip/zulip,showell/zulip,rht/zulip,susansls/zulip,jackrzhang/zulip,dawran6/zulip,vabs22/zulip,samatdav/zulip,jphilipsen05/zulip,sonali0901/zulip,andersk/zulip,brainwane/zulip,dhcrzf/zulip,Galexrt/zulip,verma-varsha/zulip,dattatreya303/zulip,blaze225/zulip,susansls/zulip,dhcrzf/zulip,andersk/zulip,timabbott/zulip,vaidap/zulip,eeshangarg/zulip,jrowan/zulip,PhilSk/zulip,zulip/zulip,amanharitsh123/zulip,amanharitsh123/zulip,eeshangarg/zulip,brockwhittaker/zulip,dawran6/zulip,verma-varsha/zulip,synicalsyntax/zulip,jphilipsen05/zulip,jackrzhang/zulip,sonali0901/zulip,shubhamdhama/zulip,rishig/zulip,j831/zulip,blaze225/zulip,mahim97/zulip,christi3k/zulip,rht/zulip,shubhamdhama/zulip,tommyip/zulip,j831/zulip,jackrzhang/zulip,showell/zulip,JPJPJPOPOP/zulip,punchagan/zulip,samatdav/zulip,sonali0901/zulip,ryanbackman/zulip,eeshangarg/zulip,jainayush975/zulip,showell/zulip,andersk/zulip,ryanbackman/zulip,shubhamdhama/zulip,andersk/zulip,timabbott/zulip,brainwane/zulip,aakash-cr7/zulip,dattatreya303/zulip,JPJPJPOPOP/zulip,rishig/zulip,sonali0901/zulip,j831/zulip,dattatreya303/zulip,sonali0901/zulip,kou/zulip,dhcrzf/zulip,mahim97/zulip,dhcrzf/zulip,susansls/zulip,brainwane/zulip,showell/zulip,souravbadami/zulip,hackerkid/zulip,susansls/zulip,verma-varsha/zulip,hackerkid/zulip,samatdav/zulip,zulip/zulip,SmartPeople/zulip,punchagan/zulip,j831/zulip,synicalsyntax/zulip,tommyip/zulip,christi3k/zulip,eeshangarg/zulip,hackerkid/zulip,JPJPJPOPOP/zulip,vaidap/zulip,brockwhittaker/zulip,jainayush975/zulip,jrowan/zulip,aakash-cr7/zulip,tommyip/zulip,rishig/zulip,SmartPeople/zulip,christi3k/zulip,amanharitsh123/zulip,jackrzhang/zulip,jphilipsen05/zulip,timabbott/zulip,susansls/zulip,jackrzhang/zulip,SmartPeople/zulip,vaidap/zulip,kou/zulip,PhilSk/zulip,j831/zulip,aakash-cr7/zulip,dattatreya303/zulip,ryanbackman/zulip,andersk/zulip,rishig/zulip,jackrzhang/zulip,timabbott/zulip,aakash-cr7/zulip,brockwhittaker/zulip,tommyip/zulip,jainayush975/zulip,SmartPeople/zulip,jrowan/zulip,punchagan/zulip,christi3k/zulip,tommyip/zulip,brainwane/zulip,timabbott/zulip,tommyip/zulip,showell/zulip,dawran6/zulip,JPJPJPOPOP/zulip,brainwane/zulip,vaidap/zulip,rishig/zulip,kou/zulip,shubhamdhama/zulip,punchagan/zulip,souravbadami/zulip,eeshangarg/zulip,mahim97/zulip,aakash-cr7/zulip,shubhamdhama/zulip,brockwhittaker/zulip,PhilSk/zulip,PhilSk/zulip,rht/zulip,dattatreya303/zulip,rht/zulip,hackerkid/zulip,vabs22/zulip,brainwane/zulip,rht/zulip,showell/zulip,souravbadami/zulip,vaidap/zulip,PhilSk/zulip,souravbadami/zulip,ryanbackman/zulip,rht/zulip,zulip/zulip,synicalsyntax/zulip,kou/zulip,jackrzhang/zulip,punchagan/zulip,zulip/zulip,susansls/zulip,jainayush975/zulip,dattatreya303/zulip,zulip/zulip,verma-varsha/zulip,hackerkid/zulip,kou/zulip,SmartPeople/zulip,Galexrt/zulip,synicalsyntax/zulip,punchagan/zulip,shubhamdhama/zulip,amanharitsh123/zulip,blaze225/zulip,vabs22/zulip,Galexrt/zulip,Galexrt/zulip,shubhamdhama/zulip,vabs22/zulip,jphilipsen05/zulip,samatdav/zulip,JPJPJPOPOP/zulip,mahim97/zulip,ryanbackman/zulip,hackerkid/zulip,punchagan/zulip,verma-varsha/zulip,synicalsyntax/zulip,christi3k/zulip,jphilipsen05/zulip,jrowan/zulip,kou/zulip,vabs22/zulip,Galexrt/zulip,dawran6/zulip,aakash-cr7/zulip,timabbott/zulip,blaze225/zulip,amanharitsh123/zulip,j831/zulip,Galexrt/zulip,dhcrzf/zulip,amanharitsh123/zulip,timabbott/zulip,ryanbackman/zulip,brockwhittaker/zulip,rishig/zulip