This creates a BlockDeviceCmd object to hold the main() function.
This doesn't really do anything different right now, but sets a base
for using argparse subparsers to handle the command-line
Change-Id: I4acf95ff4d554a3b4e7e2244ab1706631b98458f
This moves the YAML parameter parsing into the command-line driver.
It makes the argument optional so it can be taken from the environment
variable directly. The parsed YAML is passed to the BlockDevice
object.
Change-Id: I6fa5e5b7d1fccfc7cf47d6e4a1fa6e560734680d