Bug 1096332 - All content-related workflows broken on Agent

All *ContextImpl classes now user eagerly loaded plugin container services

The content subsystem was the only one affected as:
* some of the other managers were created and initialized before the inventory manager
* some of the *ContextImpl classes were still lazy loading container services

(cherry picked from commit 2f359251836f5ce82b0fcd28903e423082326051)
Signed-off-by: Lukas Krejci <lkrejci@redhat.com>
Bug 1096332 - All content-related workflows broken on Agent

Create and initialize managers in order

Passes rhq-core-plugin-container tests rhq-core-plugin-container-itest tests.
Passes manual testing of an AS7 resource:
* events
* content
* measurement
* operation
(before and after restart of the plugin container)

(cherry picked from commit aefe29a44961fc723d5241d6b67bea2f2f3ccaf7)
Signed-off-by: Lukas Krejci <lkrejci@redhat.com>