When returning list of available exports,
don't add the exports which are not accessible to requesting client

Ported from 1.5: 719ee47f03409dd51fbcb80663081679e0afbc52

Signed-off-by: suhrud <supatank@in.ibm.com>
Merge branch 'tp/showmount_S1050937' into ibm_next_20_tmp