LU-7420 echo: fix echo server to work with unified target

LU-7420 echo: fix echo server to work with unified target

After Unified Target introduction the echo server lost its
ability to serve incoming request, i.e. works like fake OFD.
Patch restores that functionality, so echo server is able to
process requests from the echo client via network.

Test-Parameters: trivial testlist=obdfilter-survey
Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Signed-off-by: Elena Gryaznova <c17455@cray.com>
Change-Id: I0c0d347486463ce320c7c66a1f85f6979b9a3681
Reviewed-on: https://review.whamcloud.com/18443
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>