Drops requests under not-so-high load

[shawninder]

When building vigour-example for ios, some image resize requests result in 408 or 504 (timeout related errors). This is happening under not-so-high load (21 simultaneous POSTs, including large files)

The requesting side should retry on timeout, but let's make sure we're doing everything possible to mitigate this.

• [ ] find a way to detect the issue in advance and respond to subsequent requests with retry-after
• [ ] check for other relevant http headers
• [ ] optimize timeout settings (express?)
• [x] optimize pooling settings (express?)
• [ ] start response before image is ready to get more time from the requester?

[shawninder]

manip function should either turn socket pooling off or, prefferably, increase maxSockets. This should also be benchmarked to prove it helps.

[shawninder]

We should also use gzip, both when retrieving the original image and when sending the result back to the caller