FileStore: Calling index->lookup() from same thread resuults osd hang
Since Index is now locked from Path constructor(). The function like
_clone() which is calling lfn_open() twice with same Index* producing
a deadlock. To fix this, lfn_open() needs to identify the it's been
called with a valid Index and thus instruct Path constructor not to
lock it.

Signed-off-by: Somnath Roy <somnath.roy@sandisk.com>