BUG: Prevent MINC transform tests outputs from clobbering.

Use different file names to prevent test failures on systems that run the
tests in parallel.

Change-Id: I397e193399fdd1600414c9fb25788279b85075e3
Merge topic 'minc-transform-outputfile'

1929776 BUG: Prevent MINC transform tests outputs from clobbering.