The default java options make the call to GenerateMIMAIgnore take
forever to run since it's gc'ing all the time. Improve things by
setting the perm gen size / max heap size to larger values.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #5615 from vanzin/gen-mima-fix and squashes the following commits:

f44e921 [Marcelo Vanzin] [minor] [build] Set java options when generating mima ignores.