fcoll/vulcan: minor code reorg

extract some code into stand alone routines in preparation for adding a vulcan read_all implementation.
Specifically, this pr adds new routines for :
 - mca_fcoll_vulcan_calc_blocklen_disps
 - mca_fcoll_vulcan_calc_file_offsets
 - mca_fcoll_vulcan_calc_io_array

which will be reused in the read_all as well.
Also, some white-space cleanup of the code.

Signed-off-by: Edgar Gabriel <[email protected]>

Author: edgargabriel