fix(tracing): make activation robust against exotic Array.find override

[basti1302]

• Make instrumentation robust against Array.prototype.find() returns -1 instead of undefined montagejs/collections#178.
• Make check for disabled instrumentation stricter (the keys provided in config.tracing.disabledTracers/INSTANA_DISABLED_TRACERS need to be an exact, case-insensitive match of the instrumentation file now). If you have used this configuration option and relied on the fact that this was a string.contains check previously, you might need to update your config.