topdown: change the tls_use_system_certs default to true

This commit changes the default of `tls_use_system_certs`
parameter for `http.send` from `false` to `true`

Fixes #2271

Signed-off-by: Olamide Omolola <omololaolamidex@gmail.com>

Fixup to commit 5c213e5

Signed-off-by: Olamide Omolola <omololaolamidex@gmail.com>

Fixed variables name changes as suggested by @anderseknert

Signed-off-by: Olamide Omolola <omololaolamidex@gmail.com>

Amended test as suggested by @srenatus

Signed-off-by: Olamide Omolola <omololaolamidex@gmail.com>