Adds basevmdk config directive

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)
updates cmdInit() to check for B2D.VMDK

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)
Adds helper to copy a specified disk image for the persistent partition

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)
Updates in-line deferred function to not return

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)
Adds named return value to copyDiskImage()

Docker-DCO-1.1-Signed-off-by: Isaac Boehman <admin@yacn.pw> (github: yacn)
Merge pull request #79 from yacn/feature/basevmdk

Adds config option to specify a base disk image for persistence partition