adding merge_config support

[fooelisa]

Noteworthy pyEOS/eos.py changes:

re-naming of compare_config based on napalm/issue/4:

• def compare_config(self):
• def compare_replace_config(self):

adding:

• def compare_merge_config(self):

and adding:

• def merge_config(self, config=None):

Sorry, I went all cleanup mode on ansible/eos_install_config while building the replace in there :)

[dbarrosop]

Shouldn´t we catch the error in the run_commands instead for consistency and reusability?

[fooelisa]

Done!