Interpolation of curly braces in arguments/env vars

Submitted as a security vulnerability because this involves mishandling of user input. It is not obvious that this is directly exploitable, but seems likely to contribute to vulnerability.

The openstack command (version 3.11.0) performs some kind of interpolation on command line arguments and environment variables that causes values enclosed in curly braces to be echoed to the terminal and not included in the variable. For example:

$ openstack nova list --os-username 'user{hello}name'
u'hello'

If the argument contains unmatched open curly braces it produces an error:

$ openstack nova list --os-username "user{name"
unmatched '{' in format