dcache: (billing) Fix incorrect MoverData field name

Regression introduced by last large multi-patch billing update.

The MoverData field 'p2p' was renamed to 'isPtp', following suggestion that Java convention be followed.  However, the liquibase and package.jdo files continued to assume the database table attribute was 'p2p'.  Hence when the data object gets dehydrated by DataNucleus, the insert statement fails.

This patch reverts the Java field name to 'p2p'.

Testing done:

Without the patch, writes to the billing database will produce the following error:

02 jul 2013 05:43:03 (billing) [] Insert of object "org.dcache.services.billing.db.data.MoverData@6e19f13" using statement "INSERT INTO "billinginfo"
("transfersize","fullsize","cellname","datestamp","protocol","action","errormessage","initiator","transaction","storageclass","errorcode","client","isp2p","pnfsid","isnew","connectiontime")
VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)" failed : user lacks privilege or object not found: isp2p
02 jul 2013 05:43:03 (billing) [] could not not commit; some billing
data may be lost

With the patch, successful srmcp produced the correct entry in billinginfo.

Note:  this has been tested on a regular instance of dcache, not using system-test.

Target: master
Patch: http://rb.dcache.org/r/5692/
Require-book: no
Require-notes: yes
Request: 2.6
Acked-by: Gerd

RELEASE NOTES:  Fixes bug preventing inserts into the billinginfo table.