simple-cipher: Add new test to check random key auto-generation
simple-cipher: Add new test to check random key auto-generation

According to the README file, a random key is to be created
when no key is provided. This key is to be composed of at
least 100 random lower-case characters.

Peque/xpython,exercism/xpython,mweb/python,de2Zotjes/xpython,exercism/xpython,pheanex/xpython,pombredanne/xpython,outkaj/xpython,rootulp/xpython,exercism/python,rootulp/xpython,N-Parsons/exercism-python,de2Zotjes/xpython,pheanex/xpython,jmluy/xpython,orozcoadrian/xpython,mweb/python,oalbe/xpython,exercism/python,oalbe/xpython,orozcoadrian/xpython,Peque/xpython,smalley/python,wobh/xpython,wobh/xpython,outkaj/xpython,N-Parsons/exercism-python,jmluy/xpython,behrtam/xpython,smalley/python,pombredanne/xpython,behrtam/xpython