Enclose command args in with_venv.sh

Sync tools/with_venv.sh from oslo, it will support argument with
blanks.

Change-Id: Ibb802b21d609ea6b54fc168b17705f06ad1cb86a
Closes-Bug: #1220937
Use Unix style LF instead of DOS style CRLF

This was causing pyflakes to fail with syntax errors on some systems:
<stdin>:22: invalid syntax

Change-Id: I57669392a5ee2a786d2a6e18a9dfd0abb054b71b
Merge "Use Unix style LF instead of DOS style CRLF"
Merge "Enclose command args in with_venv.sh"