add PETSc configuration and test support

This is a combination of 9 commits:
be silent about finding tests
add configuration parameter to find PETSc
We need to check if deal.II has PETSc support and add the compile flag
if we want PETSc.
write into detailed.log if we have PETSc
include PETSc string in build info on tester
add support for PETSc tests
rename USE_PETSC to ASPECT_USE_PETSC
update changelog.h
Merge pull request #77 from tjhei/petsc_configure

add PETSc configuration and test support