Correctly test for the HAVE_SUITESPARSE_UMFPACK
Summary
Disable tests requiring suitesparse if package was not found
Details
If the package SuiteSparse was not found the tests umfpacktest and overlappingschwarztest do not compile correctly. This is because the test code doe not disable all its code in case the package was not found. This MR corrects this and implements a hard requirement inside the tests that the SuiteSparse package component UMFPACK was found and guarantees this by a CMAKE_GUARD
in the test definition.