Watch for dynamips rom & nvram change

This monitor for change the file from dynamips by computing a
hash of the watched file.

The way dynamips work prevent the update of the modification time.

We can improve that by using native system for watching file but:
* it's require dependencies specific for each OS
* dependencies use C extensions
* this is only a backup if your router is cleanly shutdown we export
stuff

tests/utils/test_file_watcher.py

@@ -15,6 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import pytest
 import asyncio
 from unittest.mock import MagicMock
 
@@ -22,11 +23,12 @@ from unittest.mock import MagicMock
 from gns3server.utils.file_watcher import FileWatcher
 
 
-def test_file_watcher(async_run, tmpdir):
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher(async_run, tmpdir, strategy):
     file = tmpdir / "test"
     file.write("a")
     callback = MagicMock()
-    fw = FileWatcher(file, callback, delay=0.5)
+    fw = FileWatcher(file, callback, delay=0.5, strategy=strategy)
     async_run(asyncio.sleep(1))
     assert not callback.called
     file.write("b")
@@ -34,12 +36,29 @@ def test_file_watcher(async_run, tmpdir):
     callback.assert_called_with(str(file))
 
 
-def test_file_watcher_not_existing(async_run, tmpdir):
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher_not_existing(async_run, tmpdir, strategy):
     file = tmpdir / "test"
     callback = MagicMock()
-    fw = FileWatcher(file, callback, delay=0.5)
+    fw = FileWatcher(file, callback, delay=0.5, strategy=strategy)
     async_run(asyncio.sleep(1))
     assert not callback.called
     file.write("b")
     async_run(asyncio.sleep(1.5))
     callback.assert_called_with(str(file))
+
+
+@pytest.mark.parametrize("strategy", ['mtime', 'hash'])
+def test_file_watcher_list(async_run, tmpdir, strategy):
+    file = tmpdir / "test"
+    file.write("a")
+
+    file2 = tmpdir / "test2"
+
+    callback = MagicMock()
+    fw = FileWatcher([file, file2], callback, delay=0.5, strategy=strategy)
+    async_run(asyncio.sleep(1))
+    assert not callback.called
+    file2.write("b")
+    async_run(asyncio.sleep(1.5))
+    callback.assert_called_with(str(file2))