LU-12781 ptlrpc: fix inline reply buffer grow

LU-12781 ptlrpc: fix inline reply buffer grow

In req_capsule_server_grow() reply buffer can be increased
without re-allocation if has enough size already, don't do
that though if rs->rs_repbuf is a wrapper, e.g. with security
enabled. In that case re-allocation is still needed.

Re-enable test 272a in sanity.sh with SHARED_KEY

Test-Parameters: mdscount=2 mdtcount=4 envdefinitions=SHARED_KEY=true testlist=sanity,sanity-pfl
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I0632b9513f877bea989b7a61a729e2db488dcfcc
Reviewed-on: https://review.whamcloud.com/36732
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>