PS-8057: Fix initialization of general and slow log file names

https://perconadev.atlassian.net/browse/PS-8057

In case general and slow log file names are provided in config
and slow log rotation is enabled, slow_query_log_file system variable
gets initialized with general log name.

The reason of the issue is that code responsible for slow and general
logs handling have many in common and during initial log names
initialization code responsible for slow log rotation was ivoked while
initializing general log name.

To fix the issue there was a checkup added to make sure code related
to slow log rotation is not invoked while general log file name is
being processed.

Author: MrRobertYuan

mysql-test/r/percona_slow_general_log_names.result

@@ -0,0 +1,6 @@
+select @@global.slow_query_log_file;
+@@global.slow_query_log_file
+mysqld.slowlog
+select @@global.general_log_file;
+@@global.general_log_file
+mysqld.general

mysql-test/t/percona_slow_general_log_names-master.opt

@@ -0,0 +1,6 @@
+--slow_query_log=ON
+--general_log=ON
+--slow_query_log_file=mysqld.slowlog
+--general_log_file=mysqld.general
+--max_slowlog_files=10
+--max_slowlog_size=5000

mysql-test/t/percona_slow_general_log_names.test

@@ -0,0 +1,3 @@
+--replace_regex /\.\d+//
+select @@global.slow_query_log_file;
+select @@global.general_log_file;

sql/log.cc

@@ -505,12 +505,18 @@ bool File_query_log::set_file(const char *new_name) {
   if (name != nullptr) my_free(name);
 
   name = nn;
+  bool res = false;
 
-  mysql_mutex_lock(&LOCK_log);
-  cur_log_ext = 0;
-  last_removed_ext = 0;
-  bool res = set_rotated_name(false) || purge_logs();
-  mysql_mutex_unlock(&LOCK_log);
+  if (m_log_type == QUERY_LOG_SLOW) {
+    mysql_mutex_lock(&LOCK_log);
+    cur_log_ext = 0;
+    last_removed_ext = 0;
+    res = set_rotated_name(false) || purge_logs();
+    mysql_mutex_unlock(&LOCK_log);
+  } else {
+    // We can do this here since we're not actually resolving symlinks etc.
+    fn_format(log_file_name, name, mysql_data_home, "", MY_UNPACK_FILENAME);
+  }
 
   return res;
 }
@@ -2138,6 +2144,8 @@ static size_t get_last_extension(const char *const name) {
  */
 bool File_query_log::set_rotated_name(const bool need_lock) {
   DBUG_ENTER("File_query_log::set_rotated_name");
+  assert(m_log_type == QUERY_LOG_SLOW);
+
   if (need_lock) mysql_mutex_assert_owner(&LOCK_log);
 
   if (!max_slowlog_size) {
@@ -2189,6 +2197,8 @@ bool File_query_log::set_rotated_name(const bool need_lock) {
  */
 bool File_query_log::rotate(const ulong max_size) {
   DBUG_ENTER("File_query_log::rotate");
+  assert(m_log_type == QUERY_LOG_SLOW);
+
   mysql_mutex_assert_owner(&LOCK_log);
 
   if (my_b_tell(&log_file) > max_size) {
@@ -2207,6 +2217,8 @@ bool File_query_log::rotate(const ulong max_size) {
  */
 bool File_query_log::purge_logs() {
   DBUG_ENTER("File_query_log::purge_logs");
+  assert(m_log_type == QUERY_LOG_SLOW);
+
   mysql_mutex_assert_owner(&LOCK_log);
 
   if (max_slowlog_files == 0 || cur_log_ext < 1 ||