Convert deferred_delete v3 plugin to v2.1 API

Changes required to have v3 plugin natively support the V2.1
API

The force_delete action is reverted back to forceDelete

Partially implements blueprint v2-on-v3-api

Change-Id: I0b050d3328338923cf05521b9ef5cc3b1c50a586
libvirt: add validation of migration hostname

The migration hostname is substituted into the libvirt migration
URI string. If the hostname contains special characters it might
be possible to construct a malicious migration URI causing libvirt
to execute arbitrary commands as root. Protect against such a risk
by validating the hostname characters.

Change-Id: Ia3c53df1a842b5ef88f1f7ed5a3f4121df698161
Closes-bug: #1276862
Merge "libvirt: add validation of migration hostname"
Merge "Convert deferred_delete v3 plugin to v2.1 API"