Bump version to 0.15.1
Fix a typo in the program name
Remove support for OS API version 5, 10 and 15

snf-image wasn't working correctly with API versions prior to 20 anyway.
Source the variant file in the verify script

If the variant file has defined mandatory input variables like IMG_ID
the verification script should not fail to find them.

This fixes #35
Make variants.list a symlink under /etc/ganeti

This fixes #32
Change snf-image/dlurl into a URL prefix

Change the debconf variable form a URL into a url prefix. The user
will be asked to specify a prefix like this one: http://cdn.synnefo.org
and the Debian configuration scripts will create the image URL out of
it by appending /snf_image_helper_image-<VERSION>.tar.xz.

The post install script has been rewritten and this commit resolves #31
debconf: Add an update-helper question

Add a new snf-image/update-helper question. If the answer to this is
positive, the helper image is updated in post-install, according
to the URL specified in the snf-image/dlurl question.
Add postrm script

Add a postrm script to clean the helper files when purging.
In rules use devflow to get the version

Don't parse the version file. Use DEB_DEVFLOW_VERSION instead. If
we create a snapshot then the version file contains a wrong version
Make img_passwd os parameter optional

If the parameter is not defined then the ChangePassword task will not
run at all.

This resolves #34
Fix a typo in HYPERVISOR variable substitution

Many thanks to Brian Candler https://github.com/candlerb for pointing
this out. This fixes #39
Give priority to command line os parameters

OS Parameters defined as command-line arguments should overwrite the
ones given in the variants file.

Many thanks to Brian Candler https://github.com/candlerb for the
suggestion and all the help.
docs: Reflect the changes made in the hotfix

* Remove obsolete parts from the /etc/default/snf-image sample file
  shown in the configuration section.
* Update the documentation about having made the img_passwd an
  optional parameter.
Update changlog and version files for ver 0.15.1
Add a missing exit
Merge branch 'hotfix-0.15.1'
Merge branch 'debian-hotfix-0.15.1' into debian
Merge branch 'master' into debian
Bump version to 0.15.1-1~wheezy

Signed-off-by: Nikos Skalkotos <skalkoto@grnet.gr>