* removes unused filesize function
* removes ioutil usage
* updates ioutil.ReadAll to io.ReadAll
* updates ioutil.TempFile to os.CreateTemp
* updates ioutil.TempDir to os.MkdirTemp
* updates ioutil.ReadAll to os.ReadAll
* update ioutil.WriteFile to os.WriteFile
* updates ioutil.Discard to io.Discard
* updates ioutil.ReadDir to os.ReadDir where applicable
* removes unused code in idk
* creates type to use for context value keys
* replaces assert.Nil with assert.NoError for error checks
This change should have been adding the "GetClientCertificate"
function in server/tlsconfig.go. This is in addition to the
GetCertificate func which is only used by servers. It ended up being
much more involved for a few reasons:
1. We had no way of passing a configured HTTP client into the
translate store stuff.
2. Our cluster tests assumed http, not HTTPS, and didn't have any way
to pass the necessary configuration in.
3. I encountered what turned out to be an unrelated bug in
cmd/server_test.go which is why I moved "close(m.Started)" in
server/server.go. Basically, I was running something on port 10111
which caused the test to fail (because it was trying to bind to that),
but the failure was not immediately caught during server startup
because the m.Started channel got closed which allowed the test code
to fall through to where it called m.Close() which then got a nil
pointer exception because m.Handler had never been set up.
4. Our test code was assuming that it could create clients that
ignored the config, which meant they didn't do TLS. I added an
InternalClient() method to pilosa.Server to expose the configured
client.
