Middlelware to ensure request ID

The feature of the proposed middleware is simple:
* Generate request-id for each REST request
* Set the generated request-id to request environment
* Add X-OpenStack-Request-Id header to API response to return request-id

blueprint middleware-request-id

Note that to use this middleware with Context, we need to change
auth middlware so that request-id will be retreived from request env.

Change-Id: Ic7967cd62e7b743343d70f751b9238339171e013
Allow configurable ProcessLauncher liveness check

The current interval between ProcessLauncher checks of whether
a child process has exited - 0.01s - prioritizes fast respawning of
children at the expense of cpu usage.  This tradeoff may not be
appropriate for all clients of the class, so this patch makes the
interval configurable.  The current interval remains the default
to avoid changing expected behavior.

This patch was motivated by unnecessary idle cpu usage of the
Neutron service when configured to use ProcessLauncher-managed
worker processes.

Partial-Bug: #1095346

Change-Id: I2f5e06f98be1f75c21e6681967b573f5d88a4ed6
Merge "Allow configurable ProcessLauncher liveness check"
Merge "Middlelware to ensure request ID"