[bugzid:3731,3749] More granularity for exceptions

- Prepending the CloudErrorType in the exception message
- adding a protected setter for errorType (needed for 3749)
[bugzid:3731,3749] More granularity for exceptions

fix previous change: override getMessage() (instead of setting message
in constructor) to keep the errorType displayed correctly after a call
to setErrorType()
Merge pull request #95 from amynbe/2013.07

[bugzid:3731,3749] More granularity for exceptions