test/crypto: rename slave to worker

test/crypto: rename slave to worker

Modifies the scheduler tests in the crypto unit test suite
to replace the usage of the word 'slave' with the more
appropriate word 'worker'.

The scheduler test functions were modified as follows:
test_scheduler_attach_slave_op is now called
test_scheduler_attach_worker_op,
test_scheduler_detach_slave_op is
test_scheduler_detach_worker_op.

Signed-off-by: Rebecca Troy <rebecca.troy@intel.com>
Acked-by: Akhil Goyal <gakhil@marvell.com>