[UT] Speed up BE unit test (#5131)

There are some long loops and sleeps in unit tests, it will cost a
very long time to run all unit tests, especially run in TSAN mode.
This patch speed up unit tests by shortening long loops and sleeps,
on my environment all unit tests finished in 1 minite. It's useful
to do basic functional unit tests.
You can switch to run in this mode by adding a new environment variable
'DORIS_ALLOW_SLOW_TESTS'. For example, you can set:
export DORIS_ALLOW_SLOW_TESTS=1
and also you can disable it by setting:
export DORIS_ALLOW_SLOW_TESTS=0

be/test/exprs/string_functions_test.cpp

@@ -25,6 +25,7 @@
 #include "exprs/anyval_util.h"
 #include "testutil/function_utils.h"
 #include "util/logging.h"
+#include "test_util/test_util.h"
 
 namespace doris {
 
@@ -47,7 +48,7 @@ TEST_F(StringFunctionsTest, do_money_format_bench) {
     doris_udf::FunctionContext* context = new doris_udf::FunctionContext();
     StringVal expected =
             AnyValUtil::from_string_temp(context, std::string("9,223,372,036,854,775,807.00"));
-    for (int i = 0; i < 10000000; i++) {
+    for (int i = 0; i < LOOP_LESS_OR_MORE(10, 10000000); i++) {
         StringVal result =
                 StringFunctions::do_money_format(context, "922337203685477580700"); // cent
         ASSERT_EQ(expected, result);