Fix bug causing identical reshape permutations

 * When generating permutations of a reshape operator test there was
no check to ensure that the permutation was unique, this patch adds
a check to ensure that no two newShape variables are the same.
 * Added a 'escape_counter' which will break out of while loop
if it continues on for too long.

Signed-off-by: Matthew Haddon <matthew.haddon@arm.com>
Change-Id: I231eb9b546a73431835b5dc899784f69cc22a773