Make operator tests follow consistent naming scheme

 * By making the naming scheme consistent for MUL tests
(shape_type_perm_shift) we are more easily able to parse parameters.
This is the same system used for operators like RESHAPE, where perm0 is
the only permutation allowed, but it still included in the test name.
 * For multiple operators axis and axis value were split by an underscore,
Now the form is axisX in line with other parameters.

Signed-off-by: Matthew Haddon <matthew.haddon@arm.com>
Change-Id: I92e5af6fd1e2b83bdb23ac4a4ab350010aeeeccb