Hardcode SHA1 in BMC side for now

BMC side should properly look at the Open RMCP request
and do the appropriate thing.  For compatibility, just
run things exactly as they were for the moment.

Change-Id: I2b6671e8672bc1f4e9521823db9122a93405863c

pyghmi/ipmi/private/serversession.py

@@ -61,6 +61,8 @@ class ServerSession(ipmisession.Session):
                  bmc):
         # begin conversation per RMCP+ open session request
         self.uuid = uuid
+        self.currhashlib = hashlib.sha1
+        self.currhashlen = 12
         self.rqaddr = constants.IPMI_BMC_ADDRESS
         self.authdata = authdata
         self.servermode = True