Fix double linkage for tests

cmake automatically adds libraries required by a required library to the
exe linker flags. If the same dependent library is also added for the exe
and it is listed first for the exe, cmake links twice for static libs
(for a cyclic dependency it would be required and cmake can't know).
Under certain conditions (e.g. ICC 15 with static libraries and offload
enabled) this can cause linker errors. We don't have a cyclic dependency
and thus by listing libgromacs after testutils we avoid the potential
problematic double linking. Also fixes that TESTUTILS_LIBS contains
the transitive dependencies, because that is not necessary (they are anyhow
added automatically).

Change-Id: I0327b2dba0538a2c6652c484fd7be7ae4a6cfb5b