Refactor: libcrmcommon: pcmk__set_env_option() takes compat argument

Setting this argument to true maintains the existing behavior. Setting
it to false will allow us to use pcmk__set_env_option() in more places,
to replace setenv("PCMK_<option>") -- places where we don't want to
begin setting "HA_<option>".

node_start_state was documented only as PCMK_node_start_state when it
was added, so that one uses compat=false now.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>