Fix noise in logs when running test cases in OTP 19 or older
Related to an undefined gen_server:terminate/2 callback
Fix compiler warning when building test cases in OTP 19 or older
Related to an undefined gen_server:code_change/3 callback
Fix broken test cases
One because lists:join/2 is missing (OTP 18)
Another due to expecting io_lib:format to always return strings
Declare OTP 18 as the oldest supported version
Support for AES-GCM cipher only made it to crypto in OTP 18 - encrypting repo write keys crashes in OTP 17 (compilation fails in the first place - the fixes are simple but I didn't include them since they would serve no purpose.)
gen_server:terminate/2callbackgen_server:code_change/3callbacklists:join/2is missing (OTP 18)io_lib:formatto always return stringscryptoin OTP 18 - encrypting repo write keys crashes in OTP 17 (compilation fails in the first place - the fixes are simple but I didn't include them since they would serve no purpose.)