test_suite: check for command truncate to be installed
test_suite: refactoring
test_suite: fix emergency mode tests
test_suite: fix forgotten local declaration
test_suite: fix don't use oflag=direct

In the test test_suite/mars/test_cases/admin/datadev_full oflag=direct leads
to abort of the dd with "invalid argument" in the second call to
datadev_full_dd_on_device in the loop in resize_check_resize_post_conditions.