eal: add --in-memory option

eal: add --in-memory option

This command-line option will cause DPDK to operate entirely in
memory and not create any shared files at runtime, including any
shared configuration or hugetlbfs files. This is useful for debug
purposes, as well as for certain use cases like containers or
automatic memory cleanup.

Currently, this option acts as a strict superset of --no-shconf and
--huge-unlink commands.

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