poolmanager: Fixes rebalancer bug related to use of non-US locale

Rebalancer works by issuing migration commands to pools of a
pool group. The code uses String.format to build the migration
command. The formatting of floating point values is sensitive
to the default locale. For a non-US local this means that
floating points will use a comma as a decimal separator. This
will fail with the migration module.

This patch fixes the problem.

Target: trunk
Request: 2.5
Request: 2.2
Request: 1.9.12
Require-notes: yes
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/5274/
Signed-off-by: Gerd Behrmann <behrmann@nordu.net>
Merge-request: http://rt.dcache.org/Ticket/Display.html?id=7705

Conflicts:
	modules/dcache/src/main/java/org/dcache/poolmanager/Rebalancer.java