[#3831] Fixed UT build and minor nits

[#3831] Fixed UT build and minor nits

modified:   doc/sphinx/arm/dhcp6-srv.rst
modified:   doc/sphinx/arm/logging.rst
modified:   src/bin/d2/tests/d2_process_tests.sh.in
modified:   src/bin/dhcp4/tests/dhcp4_process_tests.sh.in
modified:   src/bin/dhcp6/json_config_parser.cc
modified:   src/bin/dhcp6/tests/dhcp6_process_tests.sh.in
modified:   src/hooks/dhcp/forensic_log/libloadtests/load_unload_unittests.cc
modified:   src/lib/dhcpsrv/tests/cfgmgr_unittest.cc
modified:   src/lib/hooks/hooks_parser.cc
modified:   src/lib/process/log_parser.cc
modified:   src/lib/process/log_parser.h
modified:   src/lib/testutils/env_var_wrapper.h
modified:   src/lib/util/filesystem.cc