Add CI with python 3 including trilinos

This Merge request adds a python3 build with the corresponding tests to the current CI pipeline.

A docker image including Trilinos has been created for this purpose.

Some remaining minor compatibility issues with python 3 have been fixed.

mrstlnos/tests/beam.py

@@ -229,10 +229,11 @@ def main():
 
     slv.start()
 
-    from fwk.testing import *
-    tests = CTests()
-    tests.add(CTest('faked measure', 0, 0))
-    tests.run()
+    # [RB] this code is useless
+    #import fwk.testing as tst 
+    #tests = tst.CTests()
+    #tests.add(tst.CTest('faked measure', 0, 0))
+    #tests.run()
 
 if __name__ == "__main__":
     main()