Build changes in vrouter to support dkms.

With this change, the Makefile in the dkms package will support make
without specifying any arguments (as any stand-alone module makefile
should be) in the system where the package is installed. While building
using 'SCons' (as part of standard build), we will provide arguments
to make so that it understands where to pick some files from, as they
exist in the source tree.
Merge remote-tracking branch 'github/master' into dkms
Change variable names to have more intuitive and meaningful names
- Add comments to Makefile as per review comments.
- It seems that a 'make clean', when invoked from the kernel module compilation,
cleans only the files under the module directory. So, manually cleanup sandesh
object files that were generated as part of module compilation. Also, bring those
targets outside so that they will be accessible by statements outside module
compile statements
- Remove ${ARGS}
Merge pull request #45 from Juniper/dkms

DKMS changes (post review by Raja)