refactor zerocloud test framework

move some classes to different file and use functions that are more in line with current Swift test cases
Merge pull request #76 from pkit/tests_fixes

refactor zerocloud test framework
minimal changes to support swift-2.x

the main change is in storage policies support

new configuration string was added `standalone_policies = ''` the default is to not supply anything there
that string defines which policies will be used when executing standalone jobs
the jobs that have no local object that they read from or write to
it is either web-app case or case for nodes that communicate by network channels only
Example:
  standalone_policies = silver bronze
it means that standalone jobs will be evenly distributed between nodes in silver and bronze policy

other changes include proper passing of X-Backend-Storage-Policy-Index headers and finding a correct policy for replicated jobs