Improve documentation for Oracle connector

In the Sqoop user guide [1] there is a section for how to handle "java.net.SocketException: Connection reset" errors.

This needs to be improved because the Sqoop client itself can suffer from this error message, not only the mappers.

The solution is to specify a system property to the sqoop client too, thus the sqoop command will look like (for example to a sqoop import):

sqoop import -Djava.security.egd="file:///dev/../dev/urandom" -D mapreduce.map.java.opts="-Djava.security.egd=file:///dev/../dev/urandom" <other_sqoop_arguments>

[1] https://sqoop.apache.org/docs/1.4.6/SqoopUserGuide.html#_oracle_connection_reset_errors