Check other places for arangod

[matthewvon]

"make install" for arangodb placed the arangod binary in /usr/local/sbin. arangodb does not seem to be aware:

2017/10/22 12:46:58 Starting arangodb version 0.10.0, build 71b7af9
2017/10/22 12:46:58 Cannot find arangod (expected at /usr/sbin/arangod).
2017/10/22 12:46:58 Please install ArangoDB locally or run the ArangoDB starter in docker (see README for details).

My expectation is that arangodb should check /usr/local/sbin too.