[SNMP] Extend snmp test to cover new added phyEntitySensor MIB change (…

…#3357)

Extend test_snmp_phy_entity to cover new add phyEntitySensor MIB entries in PR sonic-net/sonic-snmpagent#211

What is the motivation for this PR?
cover new added MIB entries in physical entity sensor MIB(RFC3433)

How did you do it?
Extend current test cases to check the correctness of the newly added MIB entries.

How did you verify/test it?
Run changed test_snmp_phy_entity

Signed-off-by: Kebo Liu <kebol@nvidia.com>