Should not add metadata filter rules if disable metadata proxy

The metadata filter rules should not be added into iptables if Neutron
metadata proxy is disabled.
This patchset fixes this issue by adding a condition when adding metadata
filter rules to iptables.

Closes-Bug #1224290

Change-Id: I7f14d281c31c1828a90abac8821635773238b2d0
add greenthread.sleep to increase yields

This is a stopgap Havana release.  Add eventlet greenthread.sleep to
increase thread yields.

Partially fixes: 1230407
Partially fixes: 1224001

Change-Id: I18953cf8e457ebb33780817582b4788fb5ed6f73
Merge "Should not add metadata filter rules if disable metadata proxy"
Merge "add greenthread.sleep to increase yields"