Remove unneeded suite.ini 'pretest_clean' option

Found that all currently used suite.ini files use this option enabled.
Also there is no need to have any suite of tests where snap either
log files whould be used by the next test from the previous, due to
such test schema can be easily implemented within single test file.

Author: avtikhon

lib/test.py

@@ -151,8 +151,8 @@ def execute(self, server):
         # Note: don't forget to set 'server.current_test = self' in
         # inherited classes. Crash reporting relying on that.
         server.current_test = self
-        if self.suite_ini['pretest_clean']:
-            server.pretest_clean()
+        # All the test runs must be isolated between each other on each worker.
+        server.pretest_clean()
 
     def run(self, server):
         """ Execute the test assuming it's a python program.  If the test

lib/test_suite.py

@@ -136,7 +136,6 @@ def __init__(self, suite_path, args):
                 # use old format dictionary
                 self.fragile['tests'] = self.ini['fragile']
 
-        self.parse_bool_opt('pretest_clean', False)
         self.parse_bool_opt('use_unix_sockets', False)
         self.parse_bool_opt('use_unix_sockets_iproto', False)
         self.parse_bool_opt('is_parallel', False)

test/test-app/suite.ini

@@ -2,5 +2,4 @@
 core = app
 description = application tests
 is_parallel = True
-pretest_clean = True
 use_unix_sockets_iproto = True

test/test-tarantool/suite.ini

@@ -3,5 +3,4 @@ core = tarantool
 description = tarantool tests
 script = box.lua
 use_unix_sockets = True
-pretest_clean = True
 config = engine.cfg