Made many rpc:call/4,5 calls safer if rex is down.

Created a couple of utility functions to handle do the wrapping. Most
rpc:call/4,5 that where not wrapped in a try/catch have been changed to
use the utility. Those that weren't appeared to want a crash due to
context (such as explictly matching for only the success value).

There are some dialyzer issues that were introduced, however I'm not able to see how they are related to the changes.