Add negative testing support for ew_unary operators

 * Added negative testing support for the following operators:
abs, bitwise_not, ceil, clz, exp, floor, log, logical_not, negate, reciprocal, rsqrt

Change-Id: Icc6f146c6407502520330678420951749ba2a9ef
Signed-off-by: Matthew Haddon <matthew.haddon@arm.com>