network: firewalld: query version from python client

querying firewalld version is required as firewalld interfaces (both api
and cli) are unstable.

current implementation queries firewalld version using command-line,
however, in order to query the version the firewalld service must be
started.

starting firewalld in order to detect firewalld is bad requirement,
it has also some side effects, as once firewalld is started we actually
effect the host.

new implementation uses an undocumented firewalld python library to
query the client version, which should be sufficient to our purposes.

Change-Id: I3db43d6dc808261a1f687ea29fe23bd752ffade8
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=988075
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>