test: fix hugepage file handling in EAL flags autotest

test: fix hugepage file handling in EAL flags autotest

Before 18.05, DPDK could not release memory back to the system
neither at runtime nor before shutting down. Over the course of
18.05 up to 18.11, code was introduced to release memory at
runtime, as well as an rte_eal_cleanup() function that is supposed
to release all EAL-allocated memory before shutting down DPDK.

When 3f9e31d71d63 ("test: clean up on exit") was introduced, the
test application started to use rte_eal_cleanup() to release all
used memory after execution. However, the EAL flags autotest
still relies on the old behavior of leaving stuff behind in the
hugetlbfs.

The fix is twofold. First, the test to check for leftover files
in hugetlbfs is no longer valid as it is, because test application
now removes all files from hugetlbfs after exit. However, if we
use the --legacy-mem option, then old behavior of leaving files
in hugetlbfs after execution is restored. So the first fix is to
add --legacy-mem to all the tests that expect files in hugetlbfs
to be leftover.

However, we also need to test if default memory mode *doesn't*
leave any files behind, so we also extend the test to check for
these scenarios as well. So, both memtest1 and memtest2 are run
in legacy and default mem modes, and are checked for any leftover
files that are or are not supposed to be there.

Fixes: 3f9e31d71d63 ("test: clean up on exit")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>