rbd: Code styling cleanup

rbd: Code styling cleanup

Through the years the RBD storage pool code hasn't maintained the
same or correct coding standard which applies to libvirt.

This patch doesn't change any logic in the code, it only applies
the proper coding standards to the code where possible without
making large changes.

This way the code style used in this storage pool is consistent
throughout the whole file.

Signed-off-by: Wido den Hollander <wido@widodh.nl>