tests: add id to testsuites and tests

This patch adds id property to <testsuite>s and <testcase> elements and other properties that were used to construct the id (serial-number and <guest>).

Part of TFT-2757.

Blocked by gluetool-modules!910 (merged).

Related MRs: gluetool-modules!910 (merged), oculus!80 (merged), !887 (merged)