log: append instead of create new file in logger

fixes:#523

Author: lplewa

src/utils/utils_log.c

@@ -241,7 +241,7 @@ void util_log_init(void) {
 
         memcpy(file, arg, len);
         file[len] = '\0';
-        loggerConfig.output = fopen(file, "w");
+        loggerConfig.output = fopen(file, "w+");
         if (!loggerConfig.output) {
             loggerConfig.output = stderr;
             LOG_ERR("Cannot open output file %s - logging disabled", file);

test/utils/utils_log.cpp

@@ -14,7 +14,7 @@ int fopen_count = 0;
 FILE *mock_fopen(const char *filename, const char *mode) {
     fopen_count++;
     EXPECT_STREQ(filename, expected_filename.c_str());
-    EXPECT_STREQ(mode, "w");
+    EXPECT_STREQ(mode, "w+");
     return MOCK_FILE_PTR;
 }