Fix the multinest temporary file transfer

Previously, when running with multinest on condor, there wasn't enough time given between the eviction signal and when the job was getting kicked out for the exit sequence to complete successfully. This meant that because of the link between the temporary directory and the proper path, all progress was being lost. This MR introduces a dumper function that copies over the output from the temporary directory to the proper path every time the output is updated. I have also added a method to track the sampling time across restarts. I have tested this both locally and on condor, and it works as expected.

test/sampler_test.py

@@ -767,7 +767,8 @@ class TestPymultinest(unittest.TestCase):
                         n_iter_before_update=100, null_log_evidence=-1e90,
                         max_modes=100, mode_tolerance=-1e90, seed=-1,
                         context=0, write_output=True, log_zero=-1e100,
-                        max_iter=0, init_MPI=False, dump_callback=None)
+                        max_iter=0, init_MPI=False, dump_callback='dumper')
+        self.sampler.kwargs['dump_callback'] = 'dumper' #Check like the dynesty print_func
         self.assertListEqual([1, 0], self.sampler.kwargs['wrapped_params'])  # Check this separately
         self.sampler.kwargs['wrapped_params'] = None  # The dict comparison can't handle lists
         self.assertDictEqual(expected, self.sampler.kwargs)
@@ -782,7 +783,7 @@ class TestPymultinest(unittest.TestCase):
                         n_iter_before_update=100, null_log_evidence=-1e90,
                         max_modes=100, mode_tolerance=-1e90, seed=-1,
                         context=0, write_output=True, log_zero=-1e100,
-                        max_iter=0, init_MPI=False, dump_callback=None)
+                        max_iter=0, init_MPI=False, dump_callback='dumper')
 
         for equiv in bilby.core.sampler.base_sampler.NestedSampler.npoints_equiv_kwargs:
             new_kwargs = self.sampler.kwargs.copy()
@@ -790,6 +791,7 @@ class TestPymultinest(unittest.TestCase):
             new_kwargs[
                 "wrapped_params"
             ] = None  # The dict comparison can't handle lists
+            new_kwargs['dump_callback'] = 'dumper' #test like Dynesty print_func
             new_kwargs[equiv] = 123
             self.sampler.kwargs = new_kwargs
             self.assertDictEqual(expected, self.sampler.kwargs)