item_updater: Use relative path to append OS_RELEASE_FILE

The path append behavior changed between std::experimental and
std::filesystem where appending an absolute path replaces the path
instead of appending, therefore need to use .relative_path().

This was causing the item updater to recreate the d-bus objects with
version OS_RELEASE_FILE instead of MEDIA_DIR/rofs-x/OS_RELEASE_FILE
marking the 2 versions of the system functional and with the same
version string.

Fixes openbmc/phosphor-bmc-code-mgmt#5

Tested: Verified with debug logs that the path was just OS_RELEASE_FILE
        without this change, and it was MEDIA_DIR/rofs-x/OS_RELEASE_FILE
        after this change, the version strings were correct, and only 1
        functional BMC association was created.

Change-Id: I2f81942d7fbb24e839e8f712cd2d84a80b7cd125
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
1 file changed