Flow extension uses extension manager from agent

Removed creating separate extension manager for flow extension.
Instead, have made flow extension using the same extension manager
instance which is initialized in agent. It fixes circular
extension loading in stevedore.

Closes-Bug: #1316145
Change-Id: Id339f1876168a41ca43ba7473f3ff6949a233ef3
Readme should point to Openstack, not travis-ci

The readme, leftover from when this was teeth-agent, was still pointing
at the travis-ci build. I removed that build status and added a link to
Openstack How to Contribute wiki page, so people visiting the mirror on
Github know not to create pull requests.

Change-Id: I8a82eb0e04cc35425f7856b16568f191c4c54770
Allow configdrive partition to be precreated

This adds support for copying configdrives to disks that already have
partitions enabled and labeled for configdrives. This is neccessary for
supporting configdrives on partitioning schemes we don't support yet
(like GPT) or for some future agent iteration where we create partitions
separately.

Change-Id: Iee5b87d82be08febc495aaef3272ced4f2f32235
Merge "Allow configdrive partition to be precreated"
Merge "Readme should point to Openstack, not travis-ci"
Add missing methods to base HardwareManager class

The HardwareManager class was missing a few abstract method
declarations which it is expected to have. Add those.

Change-Id: I1d07b7f08a4fc23929bc09f65b897fdfa0da1770