Fix burnin bug: Index error in pithos account_get

Bug description: pithos test assumed there are always some extra
containers in the tested pithos account and checked for their
existence, causing an Index error to be raised when starting the
test with an empty account.

Solution: Do not check for containers outside the ones created
specifically for the test.
cyclades: Fix type error

together with some PEP8 issues.
cyclades: Fix snapshots of attached volumes

Fix major bug when taking snapshots of non-root volumes. The custom
'SnapshotInstance' method of 'GanetiRAPIClient' always took a snapshot
of the root volume (index=0) of an instance, ignoring the volume that
the user requested. This resulted in always taking a snapshot of the
root volume which in many cases did not fail.
cyclades: Invalidate snapshots when job fails

Make Cyclades invalidate snapshots in case of failure to submit the job
to Ganeti, or when the job fails. In either case invalidation is
performed by marking...
TODO: Add states sto API

fixes grnet/synnefo#231
admin: Migrate from Highcharts to C3

For every chart that uses Highcharts, add its C3 counterpart below it.
The change from Highcharts to C3 is for license reasons.
admin: Lift restriction on charts

Remove `ADMIN_ENABLE_CHARTS`, as we now use C3 instead of Highcharts.
docs: Remove Admin charts section

Due to the migration from Highcharts to C3, the charts are now enabled
by default.
Revert "cyclades: Invalidate snapshots when job fails"

This reverts commit 0d1b405df358e17e369d910edc0fa9977b12bfa9 that has
been accidentally pushed remotely.
Merge branch 'release-0.16-admin-charts' of https://github.com/apyrgio/synnefo into release-0.16
admin: Make Admin base URL configurable

Add an `ADMIN_BASE_URL` setting, which works roughly the same as the
Cyclades/Astakos base URLs (minus the service registration part). The
main benefit of the `ADMIN_BASE_URL` setting is that it allows the
administrator to define the path for Admin (or lack thereof).

Also, using the `extends_path_with_slash` function, the base URL that
the administrator chooses should work with or without a slash. In the
latter case, a Django-specific redirect view will be used to redirect
the request to the URL with slash.

Finally, the addition of the `ADMIN_BASE_URL` brings also another
change. If the administrator wants to install Admin in a separate node,
he/she no longer has to choose between using as ROOT_URLCONF the
'synnefo_admin.urls' or 'synnefo_admin.admin.urls' (their main
difference was that the former had '/admin/' hard-coded).
Using simply the 'synnefo_admin.urls' should suffice,
since the `BASE_PATH` will be extracted from the `ADMIN_BASE_URL`.

Fixes apyrgio/synnefo#289
admin: Fix selection of default catalog view

Return the highest-order view type in the `ADMIN_VIEWS_ORDER` setting.
admin: Add URL test for Admin

Add a test that checks if the `ADMIN_BASE_URL` setting is used by Admin
and if we have any issues with slashes and redirections.
admin: Add tests for default catalog view
docs: Update install/admin guides

Update the install/admin guides to reflect the addition of the
`ADMIN_BASE_URL` setting. Also, add an Admin section in the CentOS
install guide.
deploy: Add `ADMIN_BASE_URL` in Admin conf

Add an `ADMIN_BASE_URL` setting in the admin.conf file. The value of
this setting is created in the same fashion as the values for
CYCLADES_BASE_URL / ASTAKOS_BASE_URL.
Mention the `ADMIN_BASE_URL` setting in Changelog