build-ceph-rpm.sh: random bit from gitbuidler-centos6-amd64

Signed-off-by: Sage Weil <sage@inktank.com>
fabfile: do not install epel on fedora

Signed-off-by: Sage Weil <sage@inktank.com>
fabfile: recheckout build dir if it is missing

Signed-off-by: Sage Weil <sage@inktank.com>
fabfile: add/fix rpm builders

Signed-off-by: Sage Weil <sage@inktank.com>
fabfile: add missing squeeze gitbuilder

Signed-off-by: Sage Weil <sage@inktank.com>