We allow characters in the ID of an ILM policy that will result in an invalid snapshot name.

For example, an ILM policy with the name `mypolicy-*` can be created, however, the generation of the snapshot name in this line:

https://github.com/elastic/elasticsearch/blob/befb6faafc9fca327fd3cea2d0ab328a521c4e65/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/GenerateSnapshotNameStep.java#L81

Results in the `mypolicy-*` being part of the snapshot name, which the snapshot service then disallows. We should strip these invalid characters from the snapshot name.
server/src/main/java/org/elasticsearch/common/Strings.java
* Convenience method to return a String array as a delimited (e.g. CSV)
     * String. E.g. useful for <code>toString()</code> implementations.
     *
     * @param arr   the array to display
     * @param delim the delimiter to use (probably a ",")
     * @return the delimited String
     */
    public static String arrayToDelimitedString(Object[] arr, String delim) {
        StringBuilder sb = new StringBuilder();
        arrayToDelimitedString(arr, delim, sb);
        return sb.toString();
    }
    public static void arrayToDelimitedString(Object[] arr, String delim, StringBuilder sb) {
        if (isEmpty(arr)) {
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            if (i > 0) {
                sb.append(delim);
            }
            sb.append(arr[i]);
        }
    }
    /**
     * Convenience method to return a String array as a CSV String.
     * E.g. useful for <code>toString()</code> implementations.
     *
     * @param arr the array to display
     * @return the delimited String
     */