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
Change main configuration file.

Add a new setting to the main config file: `main.server.scheme`. Valid values
for this config option are, for example, http and https.

By default, comment out two settings in the config file: `main.server.scheme`
and `main.server.port`. This is in line with what many venerable daemons such as
sshd and vsftpd do. This change has the potential to break code, but the
introduction of method `get_server_url` should mitigate any negative effects.

Create method `get_server_url` in module `robottelo.common.helpers`. This method
constructs the URL of the server being tested by reading `main.server.scheme`,
`main.server.hostname` and `main.server.port`. Refactor some code which,
formerly, constructed the server URL directly from the config file. If possible,
make that code use `get_server_url` instead.

Create a unit test for `get_server_url`.
Merge pull request #907 from Ichimonji10/config-file

Change main configuration file.
Merge branch 'master' of https://github.com/omaciel/robottelo