package.bbclass: Let PR server update PKGV, not PV

PV is the package version as we need it to be during the build. PKGV is the
final version as it ends up in the package, and defaults to PV.

The packager handled builds without PR-server by replacing the AUTOINC string
in PKGV, but when the PR-server is being used, the script replaces the contents
of PKGV with the PV if the PV contains "AUTOINC". Thus the packager overrides
any change to PKGV the recipe might have made.
This breaks classes like gitpkgv that provide a correctly numbered PKGV, the
number as calculated by that class will simply be replaced with a 0-based index
from the PR-server.

This patch makes the packager look at the PKGV version instead of the PV, and
update the PKGV only based on the PKGV contents as set by the recipe.

See also the discussion here:
http://lists.openembedded.org/pipermail/openembedded-core/2015-January/100329.html



From investigating the history of the code and changes in the past year, the
use of "pv" instead of "pkgv" appears to be just an oversight, introduced in:
commit b27b4382 "prs: use the PRServer to replace the BB_URI_LOCALCOUNT functionality"
A later commit 865d001d "package/prserv: Merge two similar functions into one"
silently fixed this only for the case without PR-server by using pkgv there.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Ross Burton <ross.burton@intel.com>