driver/usbstoragedriver: Change mode enum to strings

Changes the Mode enumeration to use strings instead of integers. This
will make it easier to pass the enumeration as an argument to
labgrid-client by the user.

Signed-off-by: Joshua Watt <[email protected]>

Author: JPEWdev

labgrid/driver/usbstoragedriver.py

@@ -17,8 +17,11 @@
 
 
 class Mode(enum.Enum):
-    DD = 1
-    BMAPTOOL = 2
+    DD = "dd"
+    BMAPTOOL = "bmaptool"
+
+    def __str__(self):
+        return self.value
 
 
 @target_factory.reg_driver