[CA-141792] wrap task.destroy with approriate exception handler

  db gc thread might delete task from tasks table, we should
  ignore the Not_found exception
CA-145878: make the hotfix signing key configurable

The xapi.conf file can override the hotfix signing key fingerprint
by:

  hotfix-fingerprint=<fingerprint>

This extends the FIST-point activated hotfix testing key mechanism
that we already have.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update README.md
CA-81025: Remove archived RRDs after cross-pool migration

Destroying the VM using the API and not just the database calls causes the
removal of the archived RRDs on the master.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1936 from djs55/change-hotfix-key

CA-145878: make the hotfix signing key configurable
Whitespace: Xapi_hooks.internal_host_dead_hook

$ camlp4o -printer o -no_comments ocaml/xapi/xapi_hooks.ml | md5sum
40447b4d2bbed13c5f1b97214766a41a  -
$ git checkout HEAD^
$ camlp4o -printer o -no_comments ocaml/xapi/xapi_hooks.ml | md5sum
40447b4d2bbed13c5f1b97214766a41a  -

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #2015 from simonjbeaumont/ca-81025

CA-81025: Remove archived RRDs after cross-pool migration
CA-151605: Fix race in host_dead_hook

If any tasks are destroyed or GCed after getting the list of tasks but
before finding the host to which they were forwarded, the
host_post_declare_dead hook script will not actually be called.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #2016 from johnelse/ca-151605

CA-151605: Fix race in host_dead_hook
Merge pull request #1982 from Chunjie/master

[CA-141792] wrap task.destroy with approriate exception handler