CA-120162: don't fail if the GC can't be kicked

When a VDI.delete needs to abort the GC and restart it, a deadlock might
occur which leads to reporting that VDI.delete failed while it has
partially succeeded, as the actual deletion of the VDI will happen
sooner or later. Fixing the deadlock is not straightforward, so the best
effort solution is to simply ignore such failures.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

GitHub: closes #83 on xapi-project/sm
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 journaler.py dependencies.
- Fix Makefile.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Signed-off-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>
Reviewed-by: Keith Petley <keith.petley@citrix.com>

GitHub: closes #85 on xapi-project/sm