mainapp: Detect duplicate action targets

Tested:
    Passes the unit test suite and manually verified that the daemon
    works with a normal config on a zaius machine. Also verified that it
    produces an error if configured with multiple targets for a single
    action.

Change-Id: I8fba74f5fdfeb22c465e27b478805dc1ca702cd3
Signed-off-by: William A. Kennington III <wak@google.com>
1 file changed