Moved interface part of OFJava config into SPI so that OFPlugin won't need dependency on OFJava-IMPL

Change-Id: Ia1c135c1b5d026212e400fe23844c5179d0bb06d
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>
Signed-off-by: Michal Rehak <mirehak@cisco.com>