Fix an encoding exception when creating a public_url

When using urlparse.quote, the string needs to be utf8 encoded,
or an exception is thrown.

Change-Id: I1e3d4abc136fbbbd03a54789f3df0855ceea98e1
Closes-Bug: 1346386
Co-Authored-By: Cédric Soulas <cedric.soulas@cloudwatt.com>
Merge "Fix an encoding exception when creating a public_url"