app/test: improve hash unit tests

app/test: improve hash unit tests

Add new unit test for calculating the average table utilization,
using random keys, based on number of entries that can be added
until we encounter one that cannot be added (bucket if full).

Also, replace current hash_perf unit test to see performance more clearly.
The current hash_perf unit test takes too long and add keys that
may or may not fit in the table and look up/delete that may not be
in the table. This new unit test gets a set of keys that we know
that fits in the table, and then measure the time to add/look up/delete
them.

Note that performance numbers include time to take a random key
from a pre-made array of keys, plus a quick check of return value.
Also, as stated above, expect higher numbers, as all operations
in the new unit tests will be successful, which means that
it will take more time, than mixing both successful and unsuccesful
operations.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>