Imaging gets its own directory

All of the system-level code in imageManagers and exportManagers has been
consolidated to one directory with three distinct files:

boot.py - For GRUB related code, as well as making a non-bootable disk image
bootable (By creating a new volume & copying out the data)

clean.py - Functions that involve add/remove/editing files on the disk image

convert.py - Functions that deal with moving from one architecture/provider to
another

In addition a new file called system_calls has been placed in the service level
to reduce the over-user of service/drivers/common.py
	modified:   service/drivers/common.py
	new file:   service/imaging/boot.py
	new file:   service/imaging/clean.py
	new file:   service/imaging/common.py
	new file:   service/imaging/convert.py
	new file:   service/system_calls.py
Merge branch 'master' of https://github.com/iPlantCollaborativeOpenSource/atmosphere