Added scheduler shutdown null checks.
Merge branch 'master' of https://github.com/OpenNMS/opennms
Revert "Revert "Cleaned up handling of system properties in the remote poller (server""

This reverts commit 41fc75675a805287a1d16f893177be6cd71419e0.
Cleaned up remote poller contexts slightly.
Fixed bug NMS-6052 by adding the ignoreUnresolvablePlaceholders property
to the PropertyPlaceholderConfigurer beans since there are multiple
beans in the poller backend context. When using multiple placeholder
beans, you run into this issue:

https://jira.springsource.org/browse/SPR-6428
Added another shutdown nullcheck to Threshd.
Subclassed the server side of the Spring HTTP remoting class with a
version that will store the remote host of the HTTP connection as a
thread local variable (RemoteHostHttpInvokerServiceExporter). This can
be used to record the external address of a remote poller that is behind
a NAT firewall and then display it for informational purposes in the UI.
Updated some unit tests to use system properties to override remote
poller backend settings. Fixed PropertyPlaceholderConfigurer conflicts
in poller backend tests.