US2925 add monitoring of host pNIC in OVS

US2925 add monitoring of host pNIC in OVS

- check_interface.py: renamed to check_pnic_ovs.py
- check_interface.py: check changed to use 'ip link show' command
- monitor.py: handle check name where object type contains underscore,
  specifically 'host_pnic'
- monitor.py: refactored to work as class
- monitoring_pnic.py: changed to handle either OVS or VPP
- monitoring_check_handler.py: change to allow defining hard-coded
  check_type string for file_type naming
- monitoring config templates: removed default handler

Change-Id: Iad38fa108e9ceae18a7c94b3570a8d9b836a8632
Signed-off-by: yayogev <yaronyogev@gmail.com>