qa: avoid explicit set to client mountpoint as "/"

This causes self.cephfs_mntpt to set as "/" by default which
overrides the config in ceph.conf. `test_client_cache_size`
updates ceph.conf with:

        client mountpoint = /subdir

However, the ceph-fuse mount command has --client_mountpoint explicitly
set as "/", thereby causing the root of the file system to get mounted which
confuses the test.

Fixes: http://tracker.ceph.com/issues/56446
Introduced-by: bf83eaa
Signed-off-by: Venky Shankar <vshankar@redhat.com>

qa/tasks/cephfs/fuse_mount.py

@@ -114,8 +114,8 @@ def _get_mount_cmd(self, mntopts, mntargs):
 
         self.validate_subvol_options()
 
-        assert(self.cephfs_mntpt)
-        mount_cmd += ["--client_mountpoint=" + self.cephfs_mntpt]
+        if self.cephfs_mntpt:
+            mount_cmd += ["--client_mountpoint=" + self.cephfs_mntpt]
 
         if self.cephfs_name:
             mount_cmd += ["--client_fs=" + self.cephfs_name]

qa/tasks/cephfs/kernel_mount.py

@@ -49,6 +49,8 @@ def mount(self, mntopts=None, check_status=True, **kwargs):
 
         self.setup_netns()
 
+        if not self.cephfs_mntpt:
+            self.cephfs_mntpt = '/'
         if not self.cephfs_name:
             self.cephfs_name = 'cephfs'
 

qa/tasks/cephfs/mount.py

@@ -1503,6 +1503,3 @@ def validate_subvol_options(self):
             subvol_paths = self.ctx.created_subvols[self.cephfs_name]
             path_to_mount = subvol_paths[mount_subvol_num]
             self.cephfs_mntpt = path_to_mount
-        elif not self.cephfs_mntpt:
-            # default to the "/" path
-            self.cephfs_mntpt = "/"