Eliminate blueprint for openflowplugins-impl karaf commands

Eliminate blueprint for openflowplugins-impl karaf commands

Karaf commands are refactored to use Karaf-4 new-style definitions.
We do not use karaf-services-maven-plugin, as we justs need the
Karaf-Commands directive and not all the complexity it brings to the
table.

While we are touching tests, convert them to JUnit5.

JIRA: OPNFLWPLUG-1127
Change-Id: Ie9092226457c40f6d0fcd22c39657875b70e8975
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>