config : Replace hdparm by blockdev to reread the partitions table

There is blockdev which is installed with util-linux and partprobe
installed with parted.

So, to detect the partitions table, we prefere to use :

  # blockdev --rereadpt /dev/sda

Instead :

  # hdparm -z /dev/sda
pxe & health: Adding hdparm dependency

As i removed the hdparm dep in the base profile, i should add the dep
in the pxe and health profiles.

pxe profile use hdparm to exec an hdparm -t command in the diskinfo.py
file.

  ./src/diskinfo.py:
     return dict((name, parse_hdparm_output(cmd('hdparm -t /dev/%s' % name)))
Merge pull request #27 from goldyfruit/blockdev_instead_hdparm

Use blockdev instead hdparm to reread the partitions table