Prepare the system test for tests that require a server to import
created SKR files. This means the test script needs adjustments to
take into account the directory test files are located.
In addition, the check_keys function is renamed to ksr_check_keys
because the name clashes with check_keys from kasp.sh. It also has an
extra parameter added, offset, that can be used to check ksr files that
are created in the past or future.
(cherry picked from commit 367154c1de)
ad7366853e