Eliminate port server env var, force its use always, consolidate code
diff --git a/tools/run_tests/run_microbenchmark.py b/tools/run_tests/run_microbenchmark.py
index 262c05b..a67c8468 100755
--- a/tools/run_tests/run_microbenchmark.py
+++ b/tools/run_tests/run_microbenchmark.py
@@ -44,8 +44,7 @@
 if not os.path.exists('reports'):
   os.makedirs('reports')
 
-port_server_port = 32766
-start_port_server.start_port_server(port_server_port)
+start_port_server.start_port_server()
 
 def fnize(s):
   out = ''
@@ -108,8 +107,7 @@
     if len(benchmarks) >= min(4, multiprocessing.cpu_count()):
       # run up to half the cpu count: each benchmark can use up to two cores
       # (one for the microbenchmark, one for the data flush)
-      jobset.run(benchmarks, maxjobs=max(1, multiprocessing.cpu_count()/2),
-                 add_env={'GRPC_TEST_PORT_SERVER': 'localhost:%d' % port_server_port})
+      jobset.run(benchmarks, maxjobs=max(1, multiprocessing.cpu_count()/2))
       jobset.run(profile_analysis, maxjobs=multiprocessing.cpu_count())
       jobset.run(cleanup, maxjobs=multiprocessing.cpu_count())
       benchmarks = []
@@ -117,8 +115,7 @@
       cleanup = []
   # run the remaining benchmarks that weren't flushed
   if len(benchmarks):
-    jobset.run(benchmarks, maxjobs=max(1, multiprocessing.cpu_count()/2),
-               add_env={'GRPC_TEST_PORT_SERVER': 'localhost:%d' % port_server_port})
+    jobset.run(benchmarks, maxjobs=max(1, multiprocessing.cpu_count()/2))
     jobset.run(profile_analysis, maxjobs=multiprocessing.cpu_count())
     jobset.run(cleanup, maxjobs=multiprocessing.cpu_count())
 
@@ -154,8 +151,7 @@
     if len(benchmarks) >= 20:
       # run up to half the cpu count: each benchmark can use up to two cores
       # (one for the microbenchmark, one for the data flush)
-      jobset.run(benchmarks, maxjobs=1,
-                 add_env={'GRPC_TEST_PORT_SERVER': 'localhost:%d' % port_server_port})
+      jobset.run(benchmarks, maxjobs=1)
       jobset.run(profile_analysis, maxjobs=multiprocessing.cpu_count())
       jobset.run(cleanup, maxjobs=multiprocessing.cpu_count())
       benchmarks = []
@@ -163,8 +159,7 @@
       cleanup = []
   # run the remaining benchmarks that weren't flushed
   if len(benchmarks):
-    jobset.run(benchmarks, maxjobs=1,
-               add_env={'GRPC_TEST_PORT_SERVER': 'localhost:%d' % port_server_port})
+    jobset.run(benchmarks, maxjobs=1)
     jobset.run(profile_analysis, maxjobs=multiprocessing.cpu_count())
     jobset.run(cleanup, maxjobs=multiprocessing.cpu_count())