[clang-format] Add missing test for std::function<void( int, int )>

spacing also fixed by r230473.

The fix in r230473 was done to enable fixing the spacing for
  std::function<void( int, int )>.
I did not realized that it also fixed this
issue.  Since it is fairly different from
  Deleted &operator=(const Deleted &)& = default;
fixed in r230473, it seems sensible to add the regression test for it.

Also cleaned up the test by removing duplicated code and comment, and kept
repeated test set consistent.

Result of running the new tests with r230473 backed out:
  [ RUN      ] FormatTest.ConfigurableSpacesInParentheses
  Actual: "std::function<void(int, int)> callback;"
  Expected: "std::function<void( int, int )> callback;"
  Actual: "std::function<void( int, int )> callback;"
  Expected: "std::function<void(int, int)> callback;"
  Actual: "std::function<void( int, int ) > callback;"
  Expected: "std::function<void(int, int)> callback;"
  [  FAILED  ] FormatTest.ConfigurableSpacesInParentheses (402 ms)

Result of new tests with r230473:
  [ RUN      ] FormatTest.ConfigurableSpacesInParentheses
  [       OK ] FormatTest.ConfigurableSpacesInParentheses (209 ms)

Review: http://reviews.llvm.org/D7922

Patch by Jean-Philippe Dufraigne. Thanks!

llvm-svn: 232632