Systemd support for CloudStack 4.6

[Wido den Hollander <wi...@widodh.nl>]

Hi,

Today I've spent some time in writing a systemd service file for the
(KVM) Agent and there is a PR for that now:
https://github.com/apache/cloudstack/pull/813

While working on it I found out that when writing it properly the
profile can work on both Ubuntu 16.04 (to be released) and CentOS 7.X

Ubuntu 16.04, the next LTS, will also support systemd and it is nice
that we can use one systemd profile for both CentOS and Ubuntu.

That's why I created 'packaging/systemd' since it's generic and not
distro specific.

The Agent service executes
/usr/libexec/cloudstack/cloudstack-agent-systemd-wrapper.sh which
executes Java by combining multiple environment variables.

I no longer does a detection of the Java binary. It uses
/usr/lib/jvm/jre as JAVA_HOME and users can overwrite this by extending
the systemd service.

So there are two Jira issues:

* https://issues.apache.org/jira/browse/CLOUDSTACK-8625
* https://issues.apache.org/jira/browse/CLOUDSTACK-8840

I think I can have them both fixed by Tuesday so that for CloudStack 4.6
we have proper systemd support for the Agent and Usage server under CentOS.

For Ubuntu we'll have to wait until 16.04 (April 2016) since the current
LTS (14.04) only has partial systemd support.

It releases use from JSVC since we don't have to daemonize.

I think it's a good step forward for the packaging and usage of CloudStack.

Wido