Improve python tools' shebang

Most OS don't have python3 in /usr/bin/python...

tools/blkdump.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
 # Read specified number of bytes in specified blkdev ID and spit it to stdout.
 # The proper blkdev has to be selected and placed already.

tools/memdump.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
 # Read specified number of bytes at specified memory address and dump it to
 # stdout.

tools/upload.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python3
 
 # Push specified file  to specified device and verify that the contents is
 # correct by sending a "peek" command afterwards and check the output. Errors