Append to RUBYOPT for debugger compatibility

MSP-11147

When using Rubymine's debugger, the tests would run and say there were
no tests and no break points would be hit.  It was determined that this
was due the Rubymine's debugger injecting itself into RUBYOPTS and only
working if it's first in RUBYOPT, which means that
'metasploit:framework:spec:threads:suite' must inject '-Ilib
-rmetasploit/framework/spec/threads/logger' at the end of RUBOPT instead
of the beginning.
Ignore debugger threads

MSP-11147

When using the debugger, it adds a thread that should be allowed and not
go towards the count.