release_build_handler: Fix warnings reported by pylint

 W: 47,0: Unused import re
 W: 49,0: Unused import argparse
 W: 50,0: Unused import multiprocessing
 W: 52,0: Unused import shutil
 W: 53,0: Unused import shlex
 W: 55,0: Unused import urllib
 W:310,4:handle_online_installer_build: Unused variable 'release_tools_dir'
 W:342,4:handle_offline_installer_build: Unused variable 'release_tools_dir'
 C:393,4:create_installer: Comma not followed by a space
    cmd_args = ['python','-u','create_installer.py']
                        ^^
 C:472,4:create_online_repository: Comma not followed by a space
    cmd_args = ['python','-u', 'create_installer.py', \
                        ^^
                '-c', build_job.configurations_dir, \
                '-f', build_job.configurations_file, \
                '--create-repo', \
                '-l', build_job.license, \
                '--version-number=' + build_job.version_number, \
                '-u', urlparse.urljoin(packages_base_url, build_job.license), \
                '--ifw-tools='+ build_job.ifw_tools]
 W:516,8:init_repositories: Unused variable 'base_path_testing'
 W:517,8:init_repositories: Unused variable 'url_list'

Change-Id: I4fa51f92e4382565ca4d86234a178c3044e3598a
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>