Fixing conversion double to uint8_t conversion warning in test

This warning comes from gcc 4.1 on RHEL5.

Change-Id: I60621eb46196c3e5618ac29df5c0e3ffbc4b16ed
Merge branch 'SIMPLEITK-584_FixGCC4.1Warnings' into release

* SIMPLEITK-584_FixGCC4.1Warnings:
  Fixing conversion double to uint8_t conversion warning in test