Add /var/log/pods and /var/log/containers to the mount points for kubelet

[galal-hussein]

Both mount points:

• /var/log/pods
• /var/log/containers
  should be mounted within kubelet to be able to track the pods logs using tools like fluentd.

[soumyalj]

Tested with rke version v0.0.9-dev. Each host has directories /var/log/pods and /var/log/containers.
It was verified that the directories have data for both system and user level pods.

root@soumyarketest-02:/var/log/pods# ls -ltr
total 16
drwxr-xr-x 2 root root 4096 Jan  5 23:29 45eb687f-f270-11e7-a23e-5ab0d5506cd4
drwxr-xr-x 2 root root 4096 Jan  5 23:29 487d3d53-f270-11e7-a23e-5ab0d5506cd4
drwxr-xr-x 2 root root 4096 Jan  5 23:31 8f638d84-f270-11e7-a23e-5ab0d5506cd4
drwxr-xr-x 2 root root 4096 Jan  5 23:54 c3c323a0-f273-11e7-a23e-5ab0d5506cd4
root@soumyarketest-02:/var/log/pods# cd c3c323a0-f273-11e7-a23e-5ab0d5506cd4/
root@soumyarketest-02:/var/log/pods/c3c323a0-f273-11e7-a23e-5ab0d5506cd4# ls
testcontainer_0.log
root@soumyarketest-02:/var/log/pods/c3c323a0-f273-11e7-a23e-5ab0d5506cd4# cat testcontainer_0.log 
{"log":"1:C 05 Jan 23:54:34.785 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo\r\n","stream":"stdout","time":"2018-01-05T23:54:34.790996857Z"}
{"log":"1:C 05 Jan 23:54:34.785 # Redis version=4.0.6, bits=64, commit=00000000, modified=0, pid=1, just started\r\n","stream":"stdout","time":"2018-01-05T23:54:34.791029782Z"}
{"log":"1:C 05 Jan 23:54:34.785 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf\r\n","stream":"stdout","time":"2018-01-05T23:54:34.791077597Z"}

root@soumyarketest-02:/var/log/containers# ls
k8testrc1-h77pt_default_testcontainer-db26b73d01fe53309faf4b6e85bc0d701a6b9f6fdd65832b4c5eac8449e91c2f.log
k8testrc3-zf278_default_testcontainer-7c2d541af30ff644f0bb2876b8bd7705b0d6d55159371938a0e62d129c3abb32.log
kube-dns-autoscaler-5cb4f55974-n6kjt_kube-system_autoscaler-a38783c25b8ae24e317e31a978a060597ba3a26153c80801189183fc85377964.log
kube-flannel-ckg85_kube-system_install-cni-e8683cb143ab944f7183c2b26df99f3a47b5a73762f7cd52a32d0c37db6e872a.log
kube-flannel-ckg85_kube-system_kube-flannel-a93519cf24ca2b1e522f127e6099e01001bf00285da6b441bbd15a855587a610.log