pushkey: Fix argument names

Apparently I copypasta'd the original pushkey code in the wrong way.

Change-Id: I3bcbb30c63bab263a9801000cf79794a2798e539
diff --git a/mdt/shell.py b/mdt/shell.py
index 3b78f61..cef6128 100644
--- a/mdt/shell.py
+++ b/mdt/shell.py
@@ -139,12 +139,12 @@
     def _pushOtherKey(self, client, keyfile):
         sftp = client.openSftp()
 
-        if not os.path.exists(source_keyfile):
-            print("Can't copy {0}: no such file or directory.".format(source_keyfile))
+        if not os.path.exists(keyfile):
+            print("Can't copy {0}: no such file or directory.".format(keyfile))
             return 1
 
         source_key = ''
-        with open(args[1], 'rb') as fp:
+        with open(keyfile, 'rb') as fp:
             source_key = fp.read()
 
         try:
@@ -156,7 +156,7 @@
             fp.write('\r\n')
             fp.write(source_key)
 
-        print("Key {0} pushed.".format(source_keyfile))
+        print("Key {0} pushed.".format(keyfile))
         return 0
 
     def runWithClient(self, client, args):