Simplify ssh command

Leave paramiko handle the execution of the command.
Update a CLI user test to not do any ssh connection during the import
time.
Update requirements, now we can run with the latest paramiko.
Rename BaseAPI to APITestCase
Rename BaseCLI and MetaCLI

Rename BaseCLI to CLITestCase and MetaCLI to MetaCLITestCase
Rename BaseUI to UITestCase
Move testcase classes to robottelo.test module
Merge pull request #910 from elyezer/improve-ssh-command

Simplify ssh command
Centralize logging configuration
Add docstring for robottelo.tests module.
Merge pull request #911 from elyezer/unify-test-cases

Unify test cases