[core] Correct writing of bulk data to streams

This fixes Issue #14.  We can now see data on the device cloud
in multiple streams.  Two things were changes here to match the
docs:
- Fixed capitalization of streamId to be bumpycaps
- Removed /dummy from path
- remove leading slash on streamId (matches docs)
Merge pull request #16 from swstack/dont-write-to-dummy

[core] Correct writing of bulk data to streams