[improvement] Wrap HTTPError in ConjureHTTPError with SerializableError details (#22)

<!-- PR title should start with '[fix]', '[improvement]' or '[break]' if this PR would cause a patch, minor or major SemVer bump. Omit the prefix if this PR doesn't warrant a standalone release. -->

## Before this PR
<!-- Describe the problem you encountered with the current state of the world (or link to an issue) and why it's important to fix now. -->
`HTTPError` response content was parsed hoping to find `SerializableError` contents, though didn't extract all contents and relied on deprecated fields such as message. The original `HTTPError` and a message were then wrapped in a new `HTTPError` and reraised.

## After this PR
<!-- Describe at a high-level why this approach is better. -->
1. The original `HTTPError` is wrapped in a way (`raise_from`) that is understandable to Python 3's improved traceback functionality.
2. The new `ConjureHTTPError` can be separately detected as such while maintaining a reference to its wrapped `cause`.
3. The new `ConjureHTTPError` contains attributes to access fields from `SerializableError`, as well as the `X-B3-TraceId` from response headers when possible.

<!-- Reference any existing GitHub issues, e.g. 'fixes #000' or 'relevant to #000' -->
See also #21.

Author: Andrew Higgins

.circleci/config.yml

@@ -47,14 +47,14 @@ jobs:
           command: pip install --user setuptools tox==2.9.1 tox-virtualenv-no-download
 
       - restore_cache:
-          key: tox-v2-py27-{{ checksum "tox.ini" }}
+          key: tox-v2-py27-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
 
       - run:
           name: Install tox things
           command: if [ ! -d ".tox" ]; then python -m tox -e py27 --notest; fi
 
       - save_cache:
-          key: tox-v2-py27-{{ checksum "tox.ini" }}
+          key: tox-v2-py27-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
           paths:
             - .tox
 
@@ -82,14 +82,14 @@ jobs:
           command: pip install --user setuptools tox==2.9.1 tox-virtualenv-no-download
 
       - restore_cache:
-          key: tox-v2-py3-{{ checksum "tox.ini" }}
+          key: tox-v2-py3-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
 
       - run:
           name: Install tox things
           command: if [ ! -d ".tox" ]; then python -m tox -e py3 --notest; fi
 
       - save_cache:
-          key: tox-v2-py3-{{ checksum "tox.ini" }}
+          key: tox-v2-py3-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
           paths:
             - .tox
 
@@ -114,14 +114,14 @@ jobs:
           command: pip install --user setuptools tox==2.9.1 tox-virtualenv-no-download
 
       - restore_cache:
-          key: tox-v2-mypy27-{{ checksum "tox.ini" }}
+          key: tox-v2-mypy27-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
 
       - run:
           name: Install tox things
           command: if [ ! -d ".tox" ]; then python -m tox -e mypy27 --notest; fi
 
       - save_cache:
-          key: tox-v2-mypy27-{{ checksum "tox.ini" }}
+          key: tox-v2-mypy27-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
           paths:
             - .tox
 
@@ -146,14 +146,14 @@ jobs:
           command: pip install --user setuptools tox==2.9.1 tox-virtualenv-no-download
 
       - restore_cache:
-          key: tox-v2-mypy3-{{ checksum "tox.ini" }}
+          key: tox-v2-mypy3-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
 
       - run:
           name: Install tox things
           command: if [ ! -d ".tox" ]; then python -m tox -e mypy3 --notest; fi
 
       - save_cache:
-          key: tox-v2-mypy3-{{ checksum "tox.ini" }}
+          key: tox-v2-mypy3-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
           paths:
             - .tox
 
@@ -178,14 +178,14 @@ jobs:
           command: pip install --user setuptools tox==2.9.1 tox-virtualenv-no-download
 
       - restore_cache:
-          key: tox-v2-lint-{{ checksum "tox.ini" }}
+          key: tox-v2-lint-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
 
       - run:
           name: Install tox things
           command: if [ ! -d ".tox" ]; then python -m tox -e lint --notest; fi
 
       - save_cache:
-          key: tox-v2-lint-{{ checksum "tox.ini" }}
+          key: tox-v2-lint-{{ checksum "tox.ini" }}-({ checksum "Pipfile.lock" })
           paths:
             - .tox
 

Pipfile

@@ -5,6 +5,7 @@ name = "pypi"
 
 [packages]
 "enum34" = "*"
+future = "*"
 requests = "*"
 typing = "*"
 

Pipfile.lock

@@ -13,8 +13,9 @@
 # limitations under the License.
 
 from .configuration import SslConfiguration, ServiceConfiguration
-from .requests_client import RequestsClient, Service
+from .requests_client import RequestsClient, Service, ConjureHTTPError
 
 __all__ = [
-    'SslConfiguration', 'ServiceConfiguration', 'RequestsClient', 'Service'
+    'SslConfiguration', 'ServiceConfiguration', 'RequestsClient', 'Service',
+    'ConjureHTTPError'
 ]