add options that allow for more accurate index migration

[scottbessler]

• When migrating indexes, one will usually enable dual writes and then begin a stream2es to stream old index data to the new index. In this scenario, if a new write has written a document before stream2es attempts to write it, we'd rather the write error and be skipped. This commit allows us to use the create operation to avoid overwriting existing documents with the -no-clobber flag.
• When using this option, many error-* documents would be created, allow disabling the creation of these with the --no-tee-errors flag
• Fix an issue where error counts were not properly being tracked because the error-count was being nil'd out before being added to the state
• Fix an issue where the trace log in index-bulk reported innacurate results

This will change the following default behavior:

• In order to avoid clobbering existing data, stream2es defaults to using the create operation now.

[drewr]

Thanks @scottbessler! Way to go navigating this old code...

[drewr]

Released 20151123145930466798d.