Fix NetconfMessage not sent on EmbeddedChannel
The EmbeddedChannel implementation uses built-in implementation
for event loop (EmbeddedEventLoop) which has no own executor.
The tasks placed via execute() method are queued but not executed
unless predefined events like channel closure.
Explicit triggering of pending tasks processing resolves the issue
for now, but this needs to be revisited.
JIRA: NETCONF-1106
Change-Id: Ief1d9566651c39e10310c961e5899324e73fa923
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>