This patch adds some new unit files and targets for starting instances
with nuxwdog, as well as logic within the pki-server nuxwdog module to
switch to/from the old and new systemd unit files.

It also corrects some issues found in additional testing of the nuxwdog
change scripts.

To use nuxwdog to start the instance, a user needs to do the following:

1. Create an instance normally.
2. Run: pki-server instance-nuxwdog-enable <instance_name>
3. Start the instance using:
   systemctl start pki-tomcatd-nuxwdog@<instance_name>.service

To revert the instance, simply do the following:

1. Run: pki-server instance-nuxwdog-disable <instance_name>
2. Start the instance using:
   systemctl start pki-tomcatd@<instance_name>.service

- PKI TRAC Ticket #1315 - pki-tomcatd fails to start on system boot
- PKI TRAC Ticket #1340 - pkidestroy should not remove /var/lib/pki

tomcat now uses systemd unit files.  We will reuse and customize those
files accordingly.  As a result, startup is simplified considerably -
and pkidaemon has been gutted accordingly.

We'll need to add migration scripts for older instances in a subsequent patch.

Also added SuccessExitStatus directive to unit file to ignore exit value 143.
As a result of this setting, exit status 0 is returned.

Ticket 716

Some server files in base/common have been moved to base/server for
consistency. The build scripts have been updated accordingly.