msg/Pipe: add option to restrict delay injection to specific msg type

This makes it possible to test timeouts reliably by delaying certain
messages effectively forever, but still being able to e.g. connect and
authenticate to the monitors.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
librados: check and return on error so timeouts work

Some functions could not previously return errors, but they had an
int return value, which can now receive ETIMEDOUT.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
rados: check return values for commands that can now fail

A few places were not checking the return values of commands, since
they could not fail before timeouts were added.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
qa: add script for testing rados client timeout options

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>