Tests: check for the AddressSanitizer flag during discovery

This flag is necessary to either run or skip certain tests that have
specific behavior depending on whether AddressSanitizer is enabled.

For instance, some tests may fail only when the binary is compiled
with AddressSanitizer.

test/unit/check/discover_available.py

@@ -18,6 +18,8 @@ def discover_available(unit):
         [unit['unitd'], '--version'], stderr=subprocess.STDOUT
     ).decode()
 
+    option.configure_flag['asan'] = '-fsanitize=address' in output_version
+
     # wait for controller start
 
     if Log.wait_for_record(r'controller started') is None:

test/unit/option.py

@@ -6,6 +6,7 @@ class Options:
     _options = {
         'architecture': platform.architecture()[0],
         'available': {'modules': {}, 'features': {}},
+        'configure_flag': {},
         'is_privileged': os.geteuid() == 0,
         'skip_alerts': [],
         'skip_sanitizer': False,