Refactoring ostree upgrade tests

Commit 8f826964 contain the fix of ostree commit ID parsing. Before that commit the ID contained additional suffix (".0") and thus the comparison with COMMIT_AFTER always shows a difference and the test result was always false positive: "pass".

Moved the preparation of "outdated" ostree commit into the common function prepare_outdated_commit() and store the proper ostree commit ID as starting point.

Added function check_bootcounter() to validate values from /boot/uboot.cnt.

Added function set_bootcounter() to reset the boot counter

Fix the rollback tests. Fix the check of the uboot boot counter and the test logic. Added some useful debug output.