Add support for creating vfat and iso images

This commit introduces support for creating vfat images
and iso images in ironic. Vfat images will be used for
passing information to baremetal node using virtual
media through OOB channel. Iso images will be used for
booting up baremetal nodes via virtual media.

Change-Id: I42b88da02090aec310f567642d3174d0f482b585
Implements: blueprint ironic-ilo-virtualmedia-driver