Add riemann to the index, otherwise it doesn't exist.

Fix some typos.

...otherwise the plugin will be enabled in Python 3.5+ by default.

Rules of thumb:
- glances.conf: this is the config file that comes with the source tarball.
  Touch carefully. Not for testing.
- glances-test.conf: this is the config file for testing purposes only.

Remove unused variables
No whitespace inside parentheses
Add missing whitespace around arithmetic operator
Fix indentation
Remove trailing whitespaces