LU-12773 tests: sanity test_805 Use do_facet

LU-12773 tests: sanity test_805 Use do_facet

do_node cannot really work with $SINGLEMDS, that's the
facet name.

This fixes error message below (and a following syntax error):
mds1: ssh: Could not resolve hostname mds1: Name or service not known

Lustre-change: https://review.whamcloud.com/36204
Lustre-commit: fa8b581aea27acc00f6ac48e76ec261dddf8631a

Fixes: 106abc184d8b ("LU-8856 osd: mark specific transactions netfree")
Test-Parameters: trivial fstype=zfs
Change-Id: I0d842dbccbfd934c524ae01cca7399dd52158064
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/37901
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>