Removed non portable string comparison.
Removed non portable string comparison.

Otherwise, development setups on Mac will see:

```
Failures:

  * /Users/nqnielse/workspace/go/src/github.com/intelsdi-x/swan/pkg/provisioning/local_test.go
  Line 129:
  Expected: 'sh: 1: commandThatDoesNotExists: not found
  '
  Actual:   'sh: commandThatDoesNotExists: command not found
  '
  (Should be equal)
```

intelsdi-x/swan,intelsdi-x/swan,intelsdi-x/swan