Quick fix for switch plugin initialization now that the slurmd_step process

is exec'ed.  This implementation is not ideal, because for switch/federation
the slurmd_step process needs to read in and parse the federation.conf file
every time the slurmd_step is exec'ed.

Added "switch_g_slurmctld_init", "switch_g_slurmd_init", and
"switch_g_slurmd_step_init" calls to the switch API.

NOTE:  The "switch_g_slurmctld_init" function is not yet called anywhere in
the slurmctld, but it also is not yet needed by any switch plugin.