Fix bug 1941 - Deleting of flows very slow with large number of flows
		in data store and controller connected to the network

Flow mod flag OFPFF_SEND_FLOW_REM (send flow removed msg when flow
expires or is deleted) can not be set to "false" without this patch.
Old way to set flow mod flags contains value (e.g. _sENDFLOWREM=true)
but new implementation checks only a flag occurrence for set boolean
value to true. No occurence means false but FlowConventor set a defalut
true value without explicit own value.

+ patch2 - fix FlowModFlags TESTS
+ fixed FlowConvertorTest

(cherry picked from commit 0fa45756d6ef2810a42b08fef917a36509f1bfd8)
Change-Id: I777eceefe64535825ac258d9ab52d7bee3f83a0c
Signed-off-by: Vaclav Demcak <vdemcak@cisco.com>
Signed-off-by: Michal Rehak <mirehak@cisco.com>