Addressing a DBus query crash in pldm

This update resolves a crash occurring in pldm when attempting
to retrieve the system type from the entity manager service. The
issue is resolved by implementing exception handling for potential
errors during the dbus call.

Testing:
Tested in simulator and pldm is working fine without crash.

Change-Id: I6dae2c6b5a5001b801f02d359a48acb497ad7323
Signed-off-by: Kamalkumar Patel <kamalkumar.patel@ibm.com>