remotecommand: parameterize the name of the stdio logfile

this commits permits to record the name of the stdio used
by one remotecommand into a logfile different than 'stdio'.

Signed-off-by: Ion Alberdi <ion.alberdi@intel.com>
Merge yetanotherion/buildbot:remotecommandstdio (PR #1060)

+autopep8