Implement a custom prometheus http handler in order to:
1. Support listening on a specified address as opposed to any
2. Remove the requirement on the unmaintained promhttp library
This feature comes with one limitation: if an IPv4 address is used, the
server will not listen on the IPv6-mapped address, even if IPv6 is
available. That is, dual-stacking does not work.
Solves: #1475
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Co-authored-by: Pavel Punsky <eakraly@users.noreply.github.com>
Fixes#1533 and #1534
Memsetting `turn_params.default_users_db` before reading conf file, not
after.
Because auth is read in first iteration so secret was wiped out.
# test plan
Add new test script that uses config file to setup turnserver instead of
cli arguments and confirm it works (fails without the change)
Install dependencies and build with prometheus support during CI builds
Ubuntu 16.04 has issues supporting `MHD_USE_EPOLL_INTERNAL_THREAD` so
disabling it (using SELECT)
Should not impact anything as the only reason we use Ubuntu 16.04 is to
validate build against openssl-1.0.2
Fixes #998
