LU-14177 pcc: clear PCC-RO cache from old client access

LU-14177 pcc: clear PCC-RO cache from old client access

For the purpose of the compatibility and interoperability, we have
added a PCC-RO connection flags.

To avoid inconsistent data access, MDT does not (try to) grant
layout lock to the client at the time of getattr() and open().
When an old client without PCC-RO support requests a layout lock
via a intent lock request on the file in LCM_FL_PCC_RDONLY state,
MDT needs to clear the LCM_FL_PCC_RDONLY flag on the layout first
which will invalidate all PCC-RO caches on the clients, and then
return the layout to the old client.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I69707d1ac53decaddd32bcf231b15d3565fb200f