Update checkreceipt function for python3

[danhutchings]

The checkreceipt function is using a python2 method of readPlistFromString. This results in the below exception being raised:

AttributeError: module plistlib has no attribute readPlistFromString

This results in InstallApplications always returning 0.0.0.0.0 for the pkg-version, thereby re-installing applications already installed. The fix for this is to replace readPlistFromString with loads.

import subprocess
import plistlib

packageid = com.getchef.pkg.chef

def checkreceipt(packageid):
    try:
        cmd = ["/usr/sbin/pkgutil", "--pkg-info-plist", packageid]
        proc = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        output = proc.communicate()
        receiptout = output[0]
        if receiptout:
            plist = plistlib.loads(receiptout)
            version = plist["pkg-version"]
        else:
            version = "0.0.0.0.0"
        return version
    except Exception:
        version = "0.0.0.0.0"
        return version

checkreceipt(packageid)
17.10.3