Enable parallel testing

The result of three runs on the 4 core 8 threads CPU (i7-7820HQ CPU @
2.90GHz):

In sequence:

real  0m22.549s  0m23.230s  0m23.540s
user  0m13.501s  0m14.089s  0m14.013s
sys   0m3.467s   0m3.560s   0m3.552s

Parallel:

real  0m6.709s   0m6.646s   0m6.535s
user  0m14.416s  0m14.439s  0m14.455s
sys   0m3.403s   0m3.464s   0m3.445s

Author: Totktonada

test/common/suite.ini

@@ -3,3 +3,4 @@ core = app
 description = tests different setups simultaneously
 lua_libs = lua/multirunner.lua lua/test_data_user_order.lua \
     lua/test_data_nested_record.lua
+is_parallel = True

test/extra/suite.ini

@@ -6,3 +6,4 @@ lua_libs =
     ../common/lua/test_data_nested_record.lua \
     ../testdata/array_and_map_testdata.lua \
 	../testdata/nullable_index_testdata.lua
+is_parallel = True

test/local/suite.ini

@@ -1,3 +1,4 @@
 [default]
 core = app
 description = local tests (e. g. using spaces)
+is_parallel = True

test/shard_no_redundancy/suite.ini

@@ -2,3 +2,4 @@
 core = tarantool
 description = tests on shard without redundancy
 script = master.lua
+is_parallel = True

test/shard_redundancy/suite.ini

@@ -2,3 +2,4 @@
 core = tarantool
 description = tests on shard with redundancy
 script = master.lua
+is_parallel = True