Add support for enlarging OpenBSD images

This only enlarges the partition and not the ufs file system
Add support for resizing OpenBSD UFS file systems
Run partprobe after diskpart.py

After disklabel.py enlarges the partition the kernel must be
informed about this
Use blockdev instead of partprobe after disklabel

partprobe creates the partitions by itself and since it does not
support disklabels, the disklabel partitons are not recreated
Remount every UFS partition rw just to be sure

In many cases although rw flags is passed to mount, the command
returns SUCCESS with a warning that the fs seems to be mounted ro.
Remounting rw does work.
Fix a bug in disklabel enlarge code

If the disk size is greater that 8G then the CHS value of the MBR
will overflow. We should assign a fixed CHS value for this case.
Minor pep8 error in disklabel.py
Show the partition label in diskpart -l
Remove NUL chars from the output of disklabel.py
Rewrite the MountImage task

Add code to read /etc/fstab of the *BSD images and mount the remaining
filesystems during MountImage. This only worked for Linux
Cleanup disklabel.py

Remove --print-last-linux and change some other argument names
Pin the version of openbsd-utils pkg
Merge branch 'feature-enlarge-openbsd' into develop
Add new HELPER_MEMORY parameter

This can be used to overwrite the size of the virtual RAM that will
be given to the helper VM
Check in MountImage task if /etc/fstab is present

Add an extra check to determine if the user gave the correct
ROOT_PARTITION property
docs: Update the docs to reflect current progress

* Add links for downloading NetBSD and OpenBSD images
* Remove the reference to the partition extending limitation for OpenBSD
Merge branch 'develop'
Update ChangeLog and version for 0.13
Merge branch 'master' into debian-wheezy
Bump version to 0.13-1~wheezy

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