[KARAF-2455] Add Role-based access to any OSGi Service

Role-based access is added to existing OSGi services by hiding the
original service from a clients through service registry hooks and
presenting a proxy to the service that checks the required roles before
an invocation is made.

To enable the Role-based access for services, the service needs to match
the filter in the karaf.secured.services system property (typically set
in etc/system.properties), e.g:
  karaf.secured.services = (|(objectClass=org.acme*)(foo=bar))
Only services that match this filter have Role-based access applied,
other services are left alone.

Required roles are registered through the OSGi Configuration Admin
Service. The service PID must start with org.apache.karaf.service.acl.
For enabled services configurations with matching PIDs defining a
service.guard property that matches are looked up.
Then roles associated with the current method, its signature and/or the
passed arguments are looked up. For example, take the following
configuration:
  service.guard = (objectClass=org.acme.MyServiceAPI)
  myMethod = admin, manager
A special role declaration of '*' means that role checking is disabled
for this method.
If a matching ACL is found, but no matching definition for the method
being invoked can be found, no user can invoke the method.
If no matching ACL is found, role checking is not enabled for the
service.
As with the role-based JMX access, method signatures and arguments
(either literal or regexp-based) can be matched.

When roles are checked, these are obtained from the Subject associated
with the current AccessControlContext. By default the Karaf
RolePrincipal is checked for, but other role implementations can be
supported through the following syntax:
  my.custom.RoleImpl:someRole

This commit also contains a few small corrections to the previous
commits relating to KARAF-2434 and KARAF-2435