set ASPECT_USE_PETSC for test plugins if necessary

this fixes the problems that plugins would think they have to compile
with Trilinos even though ASPECT is compiled with PETSc.
have separate plugins pick up ASPECT_USE_PETSC

Same problem as with the test plugins. Now the define ASPECT_USE_PETSC
will be set correctly if ASPECT was compiled with PETSC support.
Merge pull request #185 from tjhei/fix_petsc_plugins

Fix plugins when using PETSc
Added parameters for reference viscosity and a viscosity-scaling coefficient.
Merge branch 'morency_doin_material'
Use a random number generator that we know is predictable.

The previous version used drand48 which is not thread-safe and whose
implementation can, at least in principle, be different on different
systems. The new version is more predictable, using a member variable
and a known random number generator from the BOOST library.
fix second place that uses old random number generator
update test output
Merge branch 'bangerth_make-particle-generation-more-predictable'

(this supersedes pull request #188)

The previous version used drand48 which is not thread-safe and whose
implementation can, at least in principle, be different on different
systems. The new version is more predictable, using a member variable
and a known random number generator from the BOOST library.

Also fix test output related to these changes.
fix test output
Merge pull request #187 from tjhei/fix_test_output

fix test output
Bugfix and additional rotation angle output.
Merge pull request #186 from gassmoeller/gplates_output_fix

Bugfix and additional rotation angle output.
Merge remote-tracking branch 'geodynamics/master'