LU-473 llite: improve error for 2.x cli + 1.8 srv

LU-473 llite: improve error for 2.x cli + 1.8 srv

Improve the error message printed to the console when a 2.x client
is trying to mount a 1.8 filesystem.  More specifically, have the 2.x
client check whether the MDS supports the OBD_CONNECT_FID and
OBD_CONNECT_FULL20 flags, without which the client will not be able
to cope.  The 2.x client also does not understand the RPC structure
of 1.8 servers (mdt_body, mdt_rec, etc), but this is harder to check.

For a 2.x server, the client will configure an LMV device, so
exp_connect_flags will be zero, but in that case we also know the
server is running 2.x.

Change-Id: I935571aa0623f9311ddf0545904230721d2fad32
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1036
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>