lib/oe/distro_check: don't set empty proxy keys
If the proxies dictionary has a proxy set to None urllib will throw an exception
instead of not using a proxy (abridged stack):
File: '/home/ross/Yocto/poky/meta/lib/oe/distro_check.py', lineno: 43, function: get_links_from_url
*** 0043: with create_socket(url,d) as sock:
0044: webpage = sock.read()
File: '/home/ross/Yocto/poky/meta/lib/oe/distro_check.py', lineno: 5, function: create_socket
0003:def create_socket(url, d):
0004: import urllib
*** 0005: socket = urllib.urlopen(url, proxies=get_proxies(d))
File: '/usr/lib/python2.7/urllib.py', lineno: 87, function: urlopen
0086: if data is None:
*** 0087: return opener.open(url)
File: '/usr/lib/python2.7/urllib.py', lineno: 203, function: open
0201: else:
0202: proxy = None
*** 0203: name = 'open_' + urltype
0204: self.type = urltype
0205: name = name.replace('-', '_')
Exception: TypeError: cannot concatenate 'str' and 'NoneType' objects
Filter out unset values so that the dictionary only has valid assignments in.
Signed-off-by: Ross Burton <ross.burton@intel.com>