Add docstrings for agent.py

Does what it says.

Partial-Bug: 1367915

Change-Id: If2617f30c75c4a844c20a60afa41330daf84053a
Add support to build iso image

This script adds support to build iso image from the given
kernel and ramdisk

Change-Id: I15dd8b8663af15b4194299986792ad8e6487508b
Implements: blueprint ilo-virtualmedia-ipa
Preserve environment variables when doing sudo

This commit adds the '-E' option for all the sudo commands
in build script of agent which causes it to preserve environment
variables.

Change-Id: Ic3fbc4ee8189cc82ef99359bf61eef33dae40a5a
Closes-Bug: 1371418
Merge "Add docstrings for agent.py"
Merge "Preserve environment variables when doing sudo"
Merge "Add support to build iso image"
Add docstrings for api/ tree

Does what it says.

Partial-Bug 1367915

Change-Id: Id1a718d652f6d98e6acb1d667f42d9c3cc82aef5
Delete unused method get_agent_mac_address()

Does what it says.

Change-Id: I01e20e3a1e7317c17da6fc04ee0b0a672cf8247b
Merge "Add docstrings for api/ tree"
Merge "Delete unused method get_agent_mac_address()"
Use poll instead of threading.Event in heartbeat thread

poll() does not rely on absolute time.
This fixes an issue where the system clock may be changed, and
the heartbeat thread would stop heartbeating.

This also gives us flexibility to force a heartbeat in a later
change.

Change-Id: Ifde7b53f59788addc43a5dac95c7b6519d87e834
Closes-Bug: 1355375
Refactor image writing

What it says
Add vhd writing support

This adds a VHDUtilImageManager class that supports writing out tar
files that contain vhds. This relies on a 3rd party tool, 'vhd-util',
and patches to that utility.

A script to build vhd-util exists here:

https://github.com/comstud/libvhd-builder

That will clone the appropriate repo for vhd-util and build it, as long
as you have the correct dependencies (documented in the build script).

Change-Id: I24d7940040e5edc413469b434778409bbac0c8f3