Use vfat for timestamp

This shouldn't really be any different than what we're doing today,
but vfat in general is a much simpler filesystem. Since we have
issues with ext4, potentially discard, or something else timing out
occasionally, this may alleviate that.

Change-Id: I735716499b6d31f3f3052a06bb905510d0cbea65

tempest/common/utils/linux/remote_client.py

@@ -183,7 +183,7 @@ class RemoteClient(remote_client.RemoteClient):
         self.exec_command('sudo umount %s' % mount_path)
 
     def make_fs(self, dev_name, fs='ext4'):
-        cmd_mkfs = 'sudo mke2fs -t %s /dev/%s' % (fs, dev_name)
+        cmd_mkfs = 'sudo mkfs -t %s /dev/%s' % (fs, dev_name)
         try:
             self.exec_command(cmd_mkfs)
         except tempest.lib.exceptions.SSHExecCommandFailed:

tempest/scenario/manager.py

@@ -1129,7 +1129,7 @@ class ScenarioTest(tempest.test.BaseTestCase):
 
     def create_timestamp(self, ip_address, dev_name=None, mount_path='/mnt',
                          private_key=None, server=None, username=None,
-                         fs='ext4'):
+                         fs='vfat'):
         """Creates timestamp
 
         This wrapper utility does ssh, creates timestamp and returns the