The caller knows what step it invokes, there is no point in repeating
it in the error message. There is also no need to wrap the exception
if it's a RESTError or an ironic-lib exception already since they
are normally detailed enough.
Only leave a detailed message when an unexpected exception happens.
Change-Id: I1d8ca1e7ed1462159e4ae5f0bcf58686f6a2681c
c5fb191393