This patch modifies the postfix_queue role to add ability to configure
postfix header_checks and sender_canonical_maps.

The contents of header_checks file is controlled by the
POSTFIX_QUEUE_HEADER_CHECKS ansible variable and sender_canonical_maps
by the POSTFIX_QUEUE_SENDER_CANONICAL_MAPS variable.
Both are optional and default to blank strings
(empty configuration files).

Add box files for eucalyptus.2

Now the install happens in the current directory, with logs in a 'logs'
subdirectory.

Other improvements: curl now fails if the Vagrantfile can't be
downloaded, because the RELEASE value is invalid.  Curl also doesn't
print as large a progress bar.  The script fails early if there's no
RELEASE specified.

(cherry picked from commit 66a25250)

Pin the demo course whenever we install it

Improved argument parsing

Mark the start and end time of the installation

Improvements to install_stack.sh

Make ansible unbuffered for better experience while logging

(cherry picked from commit 8e995343)

Check for and uninstall pip packages

(cherry picked from commit f361f761)

(cherry picked from commit 276292aa)

(cherry picked from commit a8bd50f9)