ceph-nvmeof-mon fixes

ceph-nvmeof-mon fixes

Resolves: rhbz#2277947

- add validation of the map after each  map decision

  Signed-off-by: Leonid Chernin <leonidc@il.ibm.com>
  (cherry picked from commit c2f883d032c4f4cabbaccd69bce53aff9f368efa)

- added availability per gw  to the exported map

  Signed-off-by: Leonid Chernin <leonidc@il.ibm.com>
  (cherry picked from commit dbda4f7a5220c930ae1e10ff6a92287171d5e9f4)

- src/nvmeof/NVMeofGwMonitorClient.cc: panic if the monitor flags gateway as unavailable

  Signed-off-by: Alexander Indenbaum <aindenba@redhat.com>
  (cherry picked from commit e5f9eeabde506501989170e26433bd3e698a429e)

- ceph-nvmeof-mon: disconnect panic nvmeof_mon_client_disc

  * extract nvmeof_mon_client_disc conf option
  * default value 100 secs

  Signed-off-by: Alexander Indenbaum <aindenba@redhat.com>
  (cherry picked from commit 7b469988d81ca93ce0ae0694c50172bc70be20ea)

(cherry picked from commit 041933408e62a4f3be449025a7e0438efb531a2e)
Signed-off-by: Alexander Indenbaum <aindenba@redhat.com>