fix(LinstorSR): Correctly reference a variable exception (#91)

This bug is minor but it makes it difficult to understand why snapshots
fail since the initial trace is lost due to the exception caused by the
reference to the non-existing variable "e".

Signed-off-by: Damien Thenot <damien.thenot@vates.tech>

Author: Nambrok

drivers/LinstorSR.py

@@ -2514,7 +2514,7 @@ def _snapshot(self, snap_type, cbtlog=None, cbt_consistency=None):
             self.session.xenapi.VDI.set_sm_config(
                 vdi_ref, active_vdi.sm_config
             )
-        except Exception:
+        except Exception as e:
             util.logException('Failed to snapshot!')
             try:
                 self.sr._handle_interrupted_clone(