REGTEST: Add unique-id reg-test

This reg-test verifies the following behavior:

1. That unique IDs are stable (i.e. the bug fixed in 530408f976e5fe2f2f2b4b733b39da36770b566f)
2. That unique IDs can use values from the HTTP request (see https://www.mail-archive.com/haproxy@formilux.org/msg36436.html)
1 file changed