The gpmapreduce application is an optional install included via
the --enable-mapreduce configure option. The tests were however
still in src/test/regress and unconditionally included in the
ICW schedule, thus causing test failures when mapreduce wasn't
configured.

Move all gpmapreduce tests to co-locate them with the mapreduce
code and only test when configured.

Also, add a dependency on Perl for gpmapreduce in autoconf since
it's a required component.