common: don't install *.hh files on images

app-text/qpdf uses the .hh file extension for its C++ header files. We
need these for building, but not for the actual image. So let's add the
mask here, along with C headers (*.h), into INSTALL_MASK, but not
PKG_INSTALL_MASK.

BUG=chromium:588231
TEST=trybots can pass ImageTest for blacklisted packages
TEST=check that /build/${BOARD}/usr/include/qpdf/ contains '*.hh' (and
     so cups-filters can build), but they don't get deployed to image
TEST=check that there aren't any other *.hh files in our existing images
     that would get erroneously masked by this

Change-Id: I6daab7823f1c872b1f5b99d20ca3e0e7e3d3d3ad
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/346093
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/common.sh b/common.sh
index 4834f4b..b8789f2 100644
--- a/common.sh
+++ b/common.sh
@@ -422,6 +422,7 @@
   *.go
   *.la
   *.h
+  *.hh
   *.hpp
   *.h++
   *.hxx