use ExecutableFinder and find in findBinaryPath

When using open_basedir, commands such as `which`or `command`can fail
because they might try to look outside of the restricted perimeter.
Symfony's ExecutableFinder can be used instead to look in standard
locations and we can use `find` as a last resort

A better solution would be to adopt a mechanism similar to what has
been done for office documents where a configuration parameter is used
to indicate the path where the executable is to be found.