Skip TestDataFormatterStdMap on linux instead of xfailing.

Summary:
After 7181dae1248cc1b03505cca1b7c6e3dfeffefc0a, this test progresses
much further but crashes. Will skip this test while I fix this properly.

Test Plan: dotest.py -p TestDataFormatterStdMap

Reviewers: vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8361

llvm-svn: 232403