coreos-dev: Add vm-testing use flag to pull in QEMU and Xen

Experimenting with ways to do more comprehensive platform testing.
If it proves practical then we can enable this by default.

sdk_container/src/third_party/coreos-overlay/coreos-base/coreos-dev/coreos-dev-0.1.0.ebuild

@@ -9,7 +9,7 @@ HOMEPAGE="http://coreos.com"
 LICENSE="GPL-2"
 SLOT="0"
 KEYWORDS="amd64 arm x86"
-IUSE=""
+IUSE="vm-testing"
 
 # The dependencies here are meant to capture "all the packages
 # developers want to use for development, test, or debug".  This
@@ -52,4 +52,10 @@ RDEPEND="
 	sys-process/ktop
 	sys-process/procps
 	sys-process/psmisc
+	vm-testing? (
+		app-emulation/xen
+		app-emulation/xen-pvgrub
+		app-emulation/xen-tools
+		app-emulation/qemu
+	)
 	"

sdk_container/src/third_party/coreos-overlay/coreos/config/env/app-emulation/xen

@@ -0,0 +1,5 @@
+# Creating symlinks on FAT doesn't work, so don't do that
+INSTALL_MASK="${INSTALL_MASK}
+    /boot/xen-?.?.gz
+    /boot/xen-?.gz
+    /boot/xen.gz"

sdk_container/src/third_party/coreos-overlay/coreos/config/env/app-emulation/xen-tools

@@ -0,0 +1,6 @@
+# We provide xenstore as a standalone package
+INSTALL_MASK="${INSTALL_MASK}
+    /usr/bin/xenstore
+    /usr/lib/debug/usr/bin/xenstore.debug
+    /usr/lib/debug/usr/lib*/libxenstore.so*
+    /usr/lib*/libxenstore.so*"