This change modifies the behavior of OVS native and ovs-ofctl bridge
implementations so that instead of configuring the bridge only for the
required OVS protocol version, they add the required version to the
already configured versions.
To achieve this, an add_protocols method is added to the OVSBridge
class, relying on the OVSDB add_db_attribute added in
Ib6ce75846f9b13c1c33f0ced5ccc619ee7860dc1, with the behavior of
making the provided set of versions supported in addition to already
configured ones.
It is aimed to be a cleaner solution to bug 1622644 than the quickfix merge
from I4475865c4f83cb9f3e12c709af752bc490692ca3 .
After this change, the set_protocols method appears useless and is
hence marked for future removal.
Depends-On: I4386aa293f9b18d2e17b4a80d9c7da4b9b46f3c9
Change-Id: Id5ac7e6431c97fc70d8404b16f89533b6f270eee
Related-Bug: 1622644