Add support for oci-hooks to libkpod

Add new directory /etc/crio/hooks.d, where packagers can drop a json config
file to specify a hook.

The json must specify a valid executable to run.
The json must also specify which stage(s) to run the hook:
prestart, poststart, poststop
The json must specify under which criteria the hook should be launched
If the container HasBindMounts
If the container cmd matches a list of regular expressions
If the containers annotations matches a list of regular expressions.
If any of these match the the hook will be launched.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

test/hooks/checkhook.json

@@ -0,0 +1,5 @@
+{
+    "cmd" : [".*"],
+    "hook" : "HOOKSDIR/checkhook.sh",
+    "stage" : [ "prestart" ]
+}

test/hooks/checkhook.sh

@@ -0,0 +1,4 @@
+#!/bin/sh
+echo $@ >> /run/hookscheck
+read line
+echo $line >> /run/hookscheck