driver/fastbootdriver: add erase method

"fastboot erase" erases a flash partition, so add a corresponding method
for it.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

Author: Bastian-Krause

labgrid/driver/fastbootdriver.py

@@ -109,6 +109,11 @@ def flash_all(self):
         for partition in self.flash_images.keys():
             self.flash(partition)
 
+    @Driver.check_active
+    @step(args=['partition'])
+    def erase(self, partition):
+        self('erase', partition)
+
     @Driver.check_active
     @step(args=['cmd'])
     def run(self, cmd):