The value of an environment variable is always a string and any
non-empty string evals as true.  If we want to support false values in
the text we need to parse it ourselves.

This commit fixes boolean options in the django settings file: DEBUG,
IS_DEV, EMAIL_USE_TLS, BROKER_USE_SSL, and PIN_PASSCODE_ENABLED.  In
addition, AWS_S3_SECURE_URLS and AWS_QUERYSTRING_AUTH parsed the
string value but in different manner.  This commit uses the same
approach in all, for the sake of consistency.

We drop the use of distutils.util.strtobool because distutils is
deprecated and will be removed in Python 3.12 but our implementation
is compatible.

Environment variables are strings and any non-empty string evals as
true.  This commit only checks if the value is "True" and something
fancier check True or False or error would be nicer but it's messy to
do it on a dockerfile RUN command that is sh appending to a python
file.