performance-metrics: Create test image for block I/O tests from main

In this way, we can avoid create/delete large temporary files during
every iteration of block I/O performance tests. Also, we can reuse the
'init/clean_tests()' interface in the future for other setup/cleanup.

Signed-off-by: Bo Chen <chen.bo@intel.com>

performance-metrics/src/main.rs

@@ -336,6 +336,8 @@ fn run_test_with_timetout(test: &'static PerformanceTest) -> Result<String, Erro
 fn main() {
     let test_filter = env::var("TEST_FILTER").map_or("".to_string(), |o| o);
 
+    init_tests();
+
     // Run performance tests sequentially and report results (in both readable/json format)
     let mut json_output = String::new();
     for test in TEST_LIST.iter() {
@@ -352,6 +354,8 @@ fn main() {
         }
     }
 
+    cleanup_tests();
+
     // Todo: Report/upload to the metrics database
     println!("\n\nTests result in json format: \n {}", json_output);
 }