Rename and repurpose authenticator flag

If we're not automatically saving the credential,
we shouldn't be automatically loading it either.

Setting this flag now ensure the authenticator is
more testable and doesn't affect the global user
keychain.
Upgrade async testing in test case to Xcode 6

Xcode 6 provides test expectations. Our original
interface is simpler, so it's kept. It's also
modified to be more convenient for a test to opt
into HTTP stubbing.

The other benefit is things like testing code that
uses dispatch_async are no longer a problem now
that we're not manually manipulating run loops.
Minor tweak of mocking test code style

Since 'andReturn' macros have been undefined,
'and*' macros should generally be avoided to
prevent confusion. Use the actual OCMStubRecorder
methods instead.
Clean up client test for authenticated initialization

Also make service error assert helper more generic.