Allow command-line arguments to be read from a file

This change makes it possible to specify complex command-line arguments in a
file by using '@<filename>' notation. This is possible using argparse's
'fromfile_prefix_chars' option. See
<http://docs.python.org/dev/library/argparse.html#fromfile-prefix-chars>.

Change-Id: I8e90d74dcfdd66c3ac5d8082f56dd34bd0734ce5
Merge "Allow command-line arguments to be read from a file"