Use 'hydra_python_core' module in place of 'hydrus.hydraspec'

[de-sh]

Solves #86

As has been done with moving out the hydra_python_core module that used to be hydraspec, the python hydra-agent needs to be updated similarly.

Changes

• Reflected moving out of 'hydraspec' as hydra_python_core module, updated all use of same within the repo.

[chrizandr]

Looks good to me. Are there any tests we need to change as well?

[shravandoda]

Travis config needs to change. It's still installing hydrus.