Early airshipctl usage has identified the need to eject virtual media
on-demand using airshipctl in order to prevent booting from stuck media.
This change adds a command to eject all virtual media attached to a
baremetal node.
Change-Id: Id67fa00489093dcb84ce54216e0553fa6a737ea6
Signed-off-by: Drew Walters <andrew.walters@att.com>