Replace CUPS http_t connection sharing with connection-per-op.
Replace CUPS http_t connection sharing with connection-per-op.

The httpReconnect function panics occasionally with some kind
of C.free() failure (sometimes it's reported as double-free,
other times reported as invalid blah-blah).

Rather than sharing one mutex-protected connection, let's just
open a new connectin every time we call the CUPS API.
Implications:

Each operation will take 6-20 ms longer.
All operations can happen in parallel.
The buggy c.httpReconnect function is never called.

Change-Id: I15fe3e774c63ff5cecd0297cb388b6e327fd4246

swills/cups-connector,avlis/cloud-print-connector,agoode/cups-connector,agoode/cloud-print-connector,avlis/cloud-print-connector,201371192/cups-connector,avlis/cloud-print-connector,google/cloud-print-connector,avlis/cloud-print-connector,agoode/cups-connector,agoode/cloud-print-connector,swills/cups-connector,agoode/cloud-print-connector,201371192/cups-connector,google/cloud-print-connector,google/cloud-print-connector,google/cloud-print-connector,agoode/cloud-print-connector