Notary is capable of acting in offline mode, making use of cache TUF data.
When ping is not successful, notary should still be attempted without error.
Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Upstream-commit: 5e11cd43aa21a9d0eb1f5f205f05dc7b14ee4d43
Component: engine