## What changes were proposed in this pull request?

When two Breeze SparseMatrices are operated, the result matrix may contain provisional 0 values extra in rowIndices and data arrays. This causes an incoherence with the colPtrs data, but Breeze get away with this incoherence by keeping a counter of the valid data.

In spark, when this matrices are converted to SparseMatrices, Sparks relies solely on rowIndices, data, and colPtrs, but these might be incorrect because of breeze internal hacks. Therefore, we need to slice both rowIndices and data, using their counter of active data

This method is at least called by BlockMatrix when performing distributed block operations, causing exceptions on valid operations.

See http://stackoverflow.com/questions/33528555/error-thrown-when-using-blockmatrix-add

## How was this patch tested?

Added a test to MatricesSuite that verifies that the conversions are valid and that code doesn't crash. Originally the same code would crash on Spark.

Bugfix for https://issues.apache.org/jira/browse/SPARK-20687

Author: Ignacio Bermudez <ignaciobermudez@gmail.com>
Author: Ignacio Bermudez Corrales <icorrales@splunk.com>

Closes #17940 from ghoto/bug-fix/SPARK-20687.

(cherry picked from commit 06dda1d58f8670e996921e935d5f5402d664699e)
Signed-off-by: Sean Owen <sowen@cloudera.com>