Add retry_after only to exceptions supporting it

Having retry_after in HTTP response header for 403 status code caused
client to fail with TypeError exception about unexpected keyword
argument. This is related to bug in nova-api. To prevent this kind of
client problems in the future patch adds check to from_response
function to pass retry-after header only to classes that inherit
from RetryAfterException and regression unit tests.

Change-Id: I6bfc8b33eb591d30b3c647397b11100094718e13
Closes-Bug: 1365251
Corrects typos "coearse," "proejct," and "unecrypts"

Misspelling of "coerce" found in the docstring body
of method _boot from class ServerManager. Misspellings
of "project" and "unencrypts" found in docstrings
of client.py and crypto.py.

Change-Id: I052c321f3ad5e13aa57a559e2f28ec5eec32a9b4
Merge "Add retry_after only to exceptions supporting it"
Merge "Corrects typos "coearse," "proejct," and "unecrypts""