'Fetch the checksum file if not already fetched. If the checksum file
cannot be fetched from the repos then a new file is created with
the current package\'s (specified in pkg_path) checksum value in it.
Populate the local checksum dictionary with the values read from
the checksum file.
The checksum file is assumed to be present in self.pkgmgr_dir'

def _get_checksum_dict(self):

    checksum_path = self._get_checksum_file_path()
    if (not self._checksum_dict):
        try:
            try:
                self._run_command(('ls    %s' % checksum_path))
            except (error.CmdError, error.AutoservRunError):
                self.fetch_pkg(CHECKSUM_FILE, checksum_path)
        except error.PackageFetchError:
            return {}
        checksum_file_contents = self._run_command(('cat    %s' % checksum_path)).stdout
        if (not checksum_file_contents.strip()):
            return {}
        for line in checksum_file_contents.splitlines():
            (checksum, package_name) = line.split(None, 1)
            self._checksum_dict[package_name] = checksum
    return self._checksum_dict
