Citizenshell

What's Changed
* Add sleep statement by FrederikLauber in https://github.com/meuter/citizenshell/pull/16

New Contributors
* FrederikLauber made their first contribution in https://github.com/meuter/citizenshell/pull/16

**Full Changelog**: https://github.com/meuter/citizenshell/compare/2.3.1...2.3.2

- `check_xc`, `check_err`, `wait` and `log_level`) are now explicitly expected in each shell class (as opposed to being forwarded using `**kwargs`), which helps with autocompletion
- `citizenshell.__version__` now provides the version
- improved dependencies to work with legacy python 2.7
- ignore deprecation warning from `paramiko` in python 2.7
- for convenience, import all log levels from `logging` module into citizenshell namespace, e.g. you can now do:
python
from citizenshell import LocalShell, DEBUG
sh = LocalShell(log_level=DEBUG)

- `AdbShell()` now support local adb connection over USB either using the device id explicitely or implicitely if only one device is connected (similar to what `adb` does out of the box). See README.md for mode info.

Minor update release:
- merged pull request 13
- few fixes to make the test suite more robust
- extended travis to check python 3.7 and 3.8

- in TelnetShell, when executing the 'reboot' command, there was no time for the command to execute and we were directly disconnecting, so the reboot did not actually take place

Fixed potential blocking (mostly in TelnetShell). In some cases telnetlib.readline() throws and this would cause citizenshell.ShellResult to block. Now this error is properly caught. In order to make it more robust, there is a small retry mechanism which seems to avoid aborting in most cases.