add(coreos-base/oem-cloudstack): CloudStack support

Provide initial support for CloudStack.
app-emulation/docker: make the docker socket protected
update_engine: add support for post install oem hook
coreos-kernel: bump to 3.15.6
coreos-kernel: enable CONFIG_BLK_DEV_NVME

This should resolve bug #82
Merge pull request #752 from gregkh/kernel_update

Kernel update to 3.15.6 and enable NVME driver
Merge pull request #751 from marineam/core

update_engine: add support for post install oem hook
cleanup: delete lots of unused and outdated ebuilds
chore(metadata): Regenerate cache
crossdev: fix sysroot handling in pkg-config wrapper

The pkg-config wrapper re-implemented SYSROOT support because it didn't
work correctly in pkg-config before 0.24. That was released years ago so
it is time to update, custom code broke when paths were outside of /usr
so libraries installed to /lib64 broke things.

With this fixed we don't need to generate our own wrappers.

Upstream bug: https://bugs.gentoo.org/show_bug.cgi?id=517530
Merge pull request #753 from marineam/cleanup

Cleanup old ebuilds
Merge pull request #754 from marineam/dev

crossdev: fix sysroot handling in pkg-config wrapper
profiles: re-add udev to default USE flags

Reapply 943574b4, build_packages can handle the circular dependency that
this introduces between systemd and util-linux now.
profiles: do not disable perl's gdbm use flag

It appears turning off this flag does not actually prevent perl from
trying to build against gdbm. Enable the flag so dependencies are
consistent with perl's actual behavior.
iproute2: restore two mistakenly deleted patches

Commit 3d5e4758 pruned a little too deeply.
coreos-init: update with some minor fixes

- Removes ld.so.cache generator, systemd 215 does this.
- Fix udev rule for GCE compatibility.
systemd: fix build dependencies for man pages
Merge pull request #755 from marineam/dev

Misc updates/fixes
bootengine: fix install when $ROOT is /
eclass: set default portage user and group

The PORTAGE_USERNAME and PORTAGE_GRPNAME variables are not exported by
default. The SDK uses them to get portage to run builds as the
developer's uid/gid instead of portage:portage. When running outside of
the SDK use the default portage user and group.