CA-116748: Fix VSS Snapshot for 64 bit.

- Removed swig dependency by adding a new xslib.py which defines
  wrappers for the api's defined by xen.lowlevel.xs library to communicate with xenstore.
- Removed xslib.c, xslib.h, xslib.i
- Fix drivers/vss_control.
- Removed xslib dependency from srmetadata.py.
- Fix Makefile.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>