beremiz

file isExecutable
fix non-working logging at first connection to PLC after Beremiz launch

At the same time this helps to avoid exception described in 1484:d5efbb20927e.
<xsd:attribute name="Command" type="xsd:string" use="optional" default="make -C %(buildpath)s all BEREMIZSRC=%(src)s BEREMIZCFLAGS=%(cflags)s MD5=%(md5)s USE_BEREMIZ=1 FROM_BEREMIZ=1"/>