[SPARK-11587][SPARKR] Fix the summary generic to match base R

The signature is summary(object, ...) as defined in
https://stat.ethz.ch/R-manual/R-devel/library/base/html/summary.html

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #9582 from shivaram/summary-fix.