test-run-dev: Fix start_server implementation.
test-run-dev: Fix start_server implementation.

Previously, there were following problems with the implmentation:
 * Same file handle was being used to read and write. We used to do
   `seek(0)` and then `read()`. This had a chance to overwrite file
   data. Now we use different file handles to read and write data.
 * We were using text streams. Text streams cannot be used with
   `bufferring=0`. Now we use binary streams without buffering so that
   data is available for reading without any delay.

hackerkid/zulip,brainwane/zulip,punchagan/zulip,showell/zulip,andersk/zulip,zulip/zulip,kou/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,shubhamdhama/zulip,dhcrzf/zulip,rishig/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,timabbott/zulip,dhcrzf/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,shubhamdhama/zulip,brainwane/zulip,tommyip/zulip,tommyip/zulip,shubhamdhama/zulip,dhcrzf/zulip,andersk/zulip,zulip/zulip,rht/zulip,dhcrzf/zulip,timabbott/zulip,hackerkid/zulip,synicalsyntax/zulip,timabbott/zulip,tommyip/zulip,brainwane/zulip,jackrzhang/zulip,eeshangarg/zulip,jackrzhang/zulip,kou/zulip,kou/zulip,rht/zulip,hackerkid/zulip,rishig/zulip,dhcrzf/zulip,dhcrzf/zulip,showell/zulip,kou/zulip,showell/zulip,rishig/zulip,rishig/zulip,brainwane/zulip,rishig/zulip,rishig/zulip,rht/zulip,hackerkid/zulip,rishig/zulip,synicalsyntax/zulip,punchagan/zulip,eeshangarg/zulip,hackerkid/zulip,jackrzhang/zulip,jackrzhang/zulip,punchagan/zulip,jackrzhang/zulip,brainwane/zulip,jackrzhang/zulip,rht/zulip,timabbott/zulip,punchagan/zulip,andersk/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,punchagan/zulip,jackrzhang/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,tommyip/zulip,timabbott/zulip,brainwane/zulip,shubhamdhama/zulip,tommyip/zulip,eeshangarg/zulip,timabbott/zulip,hackerkid/zulip,tommyip/zulip,zulip/zulip,eeshangarg/zulip,showell/zulip,rht/zulip,andersk/zulip,synicalsyntax/zulip,shubhamdhama/zulip,shubhamdhama/zulip,zulip/zulip,andersk/zulip,brainwane/zulip,synicalsyntax/zulip,shubhamdhama/zulip,rht/zulip,dhcrzf/zulip,showell/zulip,synicalsyntax/zulip,showell/zulip,tommyip/zulip,synicalsyntax/zulip,zulip/zulip,andersk/zulip,punchagan/zulip