docs: Update CentOS installation guide

* Add note about hotplug not working on CentOS
* Add note about disabling SELinux
* Fix a minor typo
docs: Update install guides

* Change obsolete command `quota --sync` to `quota-verify`
gtools: Support Ganeti 2.10 too

Since Ganeti 2.10, the private ganeti module is installed and linked
under /etc/ganeti/share. If this path is found, include this path
in eventd.py before importing any ganeti related modules. Otherwise
import ganeti from /usr/share/ganeti.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Fix Internal Server Errors in not allowed requests

The 'api_method_not_allowed' method requires two arguments:
the request and the allowed methods to be listed in the Allow header.
However, the allowed_methods argument was missing from some calls,
resulting to unexpected failures.
This commit fixes these issues.
cyclades: Validate length of metadata