Check for unexpected characters (specifically the ones which look like

Check for unexpected characters (specifically the ones which look like
variable names) + also fix a condition that looks incorrect

Ticket:
Reviewed By: wkok
Testing Done: Tested with the failing

This was seen in a case where mako is unable to render the template
or incorrectly renders it due to user template
errors, leaving interface names with
mako variables in them. There is no easy way to
recognize and warn about these. This patch tries to warn the user
of such cases by looking for variable patterns ('$') in interface names.
(cherry picked from commit fc0d45a794a61f7e6a3fd2c2ebce3d621bf0c7b2)