ceph.spec.in: add missing buildrequires for Fedora

This patch adds two buildrequires to the ceph.spec file, that are needed
to build the rpms under Fedora. Danny Al-Gaaf commented that the
snappy-devel dependency should actually be added to the leveldb-devel
package. I will try to get that fixed too, in the mean time, this patch
does make sure Ceph builds on Fedora.

Signed-off-by: Erik Logtenberg <erik@logtenberg.eu>
ceph.spec.in: use snappy-devel only on RHEL derivatives

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph.spec.in: move junit BuildRequires to the cephfs-java subpackage

JUnit is only needed by cephfs-java. Move the BuildRequires to this
subpackage.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
ceph.spec.in: merge back JUnit handling from SUSE spec

Merge back what we have in the (open)SUSE ceph spec file for JUnit.
Add missing Requires and the package is named junit4 on some SUSE
versions.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #478 from dalgaaf/wip-da-spec-req

Fix BuildRequires in SPEC file
Reviewed-by: Gary Lowell <gary.lowell@inktank.com>