Add a configurable drain timeout

- Add a drain timeout for testing purposes
- Fix the drain test to guarantee drain timeout < request timeout
- Add a testcase to verify no connections are allowed during drain

[#69785590]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
Use the drain timeout

- Use the drain timeout
- Set the timeouts properly

[#69785590]

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>
[#71599310] Instrument proxy with dropsonde metrics library

Signed-off-by: John Foley <jfoley@pivotallabs.com>
updates for instrumentation

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>