COMP: Mark DeformableRegistration6Test as RUNS_LONG.

This prevents Timeout test failures for the Debug/Coverage builds on the
dashboard.

Change-Id: I498f8b04627dcbd2d380bc3c3f08d0fc0e830afb
Merge topic 'DeformableRegistration6TestRunsLong'

09994b3c COMP: Mark DeformableRegistration6Test as RUNS_LONG.