Format json output properly
Format json output properly

str(dict) or print(dict) format a dict value into an invalid json
string because it uses single quotes(') instead of double quotes(").

This also fixes the log messages which mentions 'JSON' but doesn't
convert a dict value to a valid json string.

Closes-Bug: #1973566
Change-Id: I2398e3881310746f349e2c9a89c64956efbc13b2

openstack/os-net-config