Runs s3 storagedriver tests against all regions (excluding gov)
Uses random paths with slashes for storagedriver tests, adds edge cases

This replaces only using flat filenames, to better test nested file
behaviors.
Fixed inmemory/mfs.go and filesystem/driver.go after finding bugs with
the new tests and test behavior.
Merge pull request #833 from stevvooe/next-generation

Address bug in inmemory filesystem WriteAt method
Fixes normalization of inmemory file paths

A normalized path always begins with "/" and never has a trailing slash
unless it is the root directory.
Makes circle.yml run tests with the "-test.short" flag

This is due to longer tests which require more storage/memory than is
granted to us by the circle test runner vms.
Merge pull request #832 from BrianBland/ng-storagedriver-tests

Updates storagedriver tests to better test directory trees
Merge pull request #834 from stevvooe/next-generation

Implement tags HTTP API handler