moved master argument parsing to CreateSlaveOptions class

Moved the code that validates and parses 'buildbot create-slave'
master argument to runner.CreateSlaveOptions class.
slave cli: replaced Maker class with local functions

No point in creating a single instance of Maker class, we can as well
call some local functions.
catch IO errors when doing 'buildslave create-slave'

When creating buildslave directory with 'buildslave create-slave'
command, catch IO errors and print user friendly error messages.
added unit tests on buildslave.scripts.create_slave.createSlave()
added unit tests on buildslave.scripts.create_slave._makeBaseDir()
added unit tests on buildslave.scripts.create_slave._makeBuildbotTac()