Implements a default timeout of 5 seconds on the Grouper REST Client (passed through to Ruby REST Client, etc.).
Can be overridden in config "timeout" key.
As an internal implementation detail, changed the private class method `client' to yield the Grouper REST Client Resource, which receives a block.  Error/OK status is checked on responses as appropriate.
Fixes #427.
Rescue from DulHydra::Error (raised when not configured)
Merge pull request #448 from duke-libraries/issue-427

Implements a default timeout of 5 seconds on the Grouper REST Client (pa...