LU-11835 mdt: return DOM size on open resend

LU-11835 mdt: return DOM size on open resend

DOM size is returned along with DOM lock always, but it is
not true with open resend.

Patch fixes that issue and adds test case.

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I73d43933f781f192e9aa8c6ee388a043dab5bde9
Reviewed-on: https://review.whamcloud.com/34044
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>