Now that hclog can independently set levels on related loggers, we can
separate the log levels for different subsystems in terraform.
This adds the new environment variables, `TF_LOG_CORE` and
`TF_LOG_PROVIDER`, which each take the same set of log level arguments,
and only applies to logs from that subsystem. This means that setting
`TF_LOG_CORE=level` will not show logs from providers, and
`TF_LOG_PROVIDER=level` will not show logs from core. The behavior of
`TF_LOG` alone does not change.
While it is not necessarily needed since the default is to disable logs,
there is also a new level argument of `off`, which reflects the
associated level in hclog.
Use a separate log sink to always capture trace logs for the panicwrap
handler to write out in a crash log.
This requires creating a log file in the outer process and passing that
path to the child process to log to.
Use a single log writer instance for all std library logging.
Setup the std log writer in the logging package, and remove boilerplate
from test packages.
