test: idempotent filestore test failure

Remove obsolete use of collection_move()
Allow operations to be skipped if random selections don't make sense
Track total number of possible objects in m_num_objects
BUG: do_remove() was calling _do_touch() instead of _do_remove()
Operations that require an object select from among existing objects in collection
Initialize m_num_objects unique objects across collections

touch: don't create an object that already exists in another collection
remove: Use remove_obj() to clear object from m_objects to have accurate tracking
clone/clone_range(): Select 2 existing objects in the collection
add: Skip operation if selected target object name exists in target collection
move: Removed this buggy operation that is only present for upgrades

fixes: #5371

Signed-off-by: David Zafman <david.zafman@inktank.com>