Handle keyring.ErrNotFound error instead of panicing.
Handle keyring.ErrNotFound error instead of panicing.

github.com/tmc/keyring returns keyring.ErrNotFound instead of a blank password
in newer libraries. Handle this case properly by nulling the error, to give the
user a chance to set a new password.

go-jira/jira,go-jira/jira,Netflix-Skunkworks/go-jira,Netflix-Skunkworks/go-jira,Netflix-Skunkworks/go-jira