fs inspector support for namazu container

[AkihiroSuda]

Fix #161

PTAL @v01dstar

How to test:

$ cat > /tmp/container.toml << EOF
explorePolicy = "random"
[explorePolicyParam]
  maxInterval = "3000ms"
  faultActionProbability = 0.5

[container]
  enableProcInspector = false
  enableFSInspector = true
EOF
$ docker pull alpine
$ mkdir /tmp/foo && echo something > /tmp/foo/bar
$ sudo ./bin/nmz container run -it --rm -v /tmp/foo:/foo --nmz-autopilot /tmp/container.toml alpine sh
container# ls /foo (sometimes slow, sometimes EIO)

[coveralls]

Coverage decreased (-0.3%) to 40.301% when pulling 8943710 on suda/wip into 96d5f13 on master.

[v01dstar]

LGTM