virttest: Support status_test_command parameter in remote.remote_login().

Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.utils_netperf: Update is_target_running() function.

Current function may fail in some situation.

Also update status_test_command parameter for the remote session.

Signed-off-by: Feng Yang <fyang@redhat.com>
Merge pull request #1905 from FengYang/utils_netperf

Utils netperf