Get primary variables and fluid state from Python

Added methods to Python module opm.simulators.BlackOilSimulator to
access primary variables and fluid state variables.

python/test/test_primary_variables.py

@@ -0,0 +1,43 @@
+import os
+import unittest
+from pathlib import Path
+from opm.simulators import BlackOilSimulator
+from .pytest_common import pushd
+
+class TestBasic(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        # NOTE: See comment in test_basic.py for the reason why we are
+        #   only using a single test_all() function instead of splitting
+        #   it up in multiple test functions
+        test_dir = Path(os.path.dirname(__file__))
+        cls.data_dir = test_dir.parent.joinpath("test_data/SPE1CASE1a")
+
+
+    def test_all(self):
+        with pushd(self.data_dir):
+            sim = BlackOilSimulator("SPE1CASE1.DATA")
+            sim.step_init()
+            sim.step()
+            pressure = sim.get_primary_variable(variable='pressure')
+            self.assertAlmostEqual(pressure[0], 41729978.837, places=2, msg='value of pressure')
+            pressure_meaning = sim.get_primary_variable_meaning(
+                variable='pressure')
+            pressure_meaning_map = sim.get_primary_variable_meaning_map(
+                variable='pressure')
+            self.assertEqual(pressure_meaning[0], pressure_meaning_map["Po"])
+            water_meaning = sim.get_primary_variable_meaning(
+                variable='water')
+            water_meaning_map = sim.get_primary_variable_meaning_map(
+                variable='water')
+            self.assertEqual(water_meaning[0], water_meaning_map["Sw"])
+            gas_meaning = sim.get_primary_variable_meaning(
+                variable='gas')
+            gas_meaning_map = sim.get_primary_variable_meaning_map(
+                variable='gas')
+            self.assertEqual(gas_meaning[0], gas_meaning_map["Sg"])
+            brine_meaning = sim.get_primary_variable_meaning(
+                variable='brine')
+            brine_meaning_map = sim.get_primary_variable_meaning_map(
+                variable='brine')
+            self.assertEqual(brine_meaning[0], brine_meaning_map["Disabled"])