Allow more proxy bypass patterns

The current restriction on proxy bypass pattern is harsh. For instance,
"*google.com" is allowed, but "*.google.com" is not. We loosen the validity
check to allow patterns like "*.cnn.com", "*.google*.com", "10.20.*.*".

bug: 13287210
Change-Id: I7551150f785cd087c963f3a8f4c9d05f0002ff04